| .. _todo: |
| |
| ========= |
| TODO list |
| ========= |
| |
| This section contains a list of smaller janitorial tasks in the kernel DRM |
| graphics subsystem useful as newbie projects. Or for slow rainy days. |
| |
| Difficulty |
| ---------- |
| |
| To make it easier task are categorized into different levels: |
| |
| Starter: Good tasks to get started with the DRM subsystem. |
| |
| Intermediate: Tasks which need some experience with working in the DRM |
| subsystem, or some specific GPU/display graphics knowledge. For debugging issue |
| it's good to have the relevant hardware (or a virtual driver set up) available |
| for testing. |
| |
| Advanced: Tricky tasks that need fairly good understanding of the DRM subsystem |
| and graphics topics. Generally need the relevant hardware for development and |
| testing. |
| |
| Expert: Only attempt these if you've successfully completed some tricky |
| refactorings already and are an expert in the specific area |
| |
| Subsystem-wide refactorings |
| =========================== |
| |
| Remove custom dumb_map_offset implementations |
| --------------------------------------------- |
| |
| All GEM based drivers should be using drm_gem_create_mmap_offset() instead. |
| Audit each individual driver, make sure it'll work with the generic |
| implementation (there's lots of outdated locking leftovers in various |
| implementations), and then remove it. |
| |
| Contact: Simona Vetter, respective driver maintainers |
| |
| Level: Intermediate |
| |
| Convert existing KMS drivers to atomic modesetting |
| -------------------------------------------------- |
| |
| 3.19 has the atomic modeset interfaces and helpers, so drivers can now be |
| converted over. Modern compositors like Wayland or Surfaceflinger on Android |
| really want an atomic modeset interface, so this is all about the bright |
| future. |
| |
| There is a conversion guide for atomic [1]_ and all you need is a GPU for a |
| non-converted driver. The "Atomic mode setting design overview" series [2]_ |
| [3]_ at LWN.net can also be helpful. |
| |
| As part of this drivers also need to convert to universal plane (which means |
| exposing primary & cursor as proper plane objects). But that's much easier to |
| do by directly using the new atomic helper driver callbacks. |
| |
| .. [1] https://blog.ffwll.ch/2014/11/atomic-modeset-support-for-kms-drivers.html |
| .. [2] https://lwn.net/Articles/653071/ |
| .. [3] https://lwn.net/Articles/653466/ |
| |
| Contact: Simona Vetter, respective driver maintainers |
| |
| Level: Advanced |
| |
| Clean up the clipped coordination confusion around planes |
| --------------------------------------------------------- |
| |
| We have a helper to get this right with drm_plane_helper_check_update(), but |
| it's not consistently used. This should be fixed, preferably in the atomic |
| helpers (and drivers then moved over to clipped coordinates). Probably the |
| helper should also be moved from drm_plane_helper.c to the atomic helpers, to |
| avoid confusion - the other helpers in that file are all deprecated legacy |
| helpers. |
| |
| Contact: Ville Syrjälä, Simona Vetter, driver maintainers |
| |
| Level: Advanced |
| |
| Improve plane atomic_check helpers |
| ---------------------------------- |
| |
| Aside from the clipped coordinates right above there's a few suboptimal things |
| with the current helpers: |
| |
| - drm_plane_helper_funcs->atomic_check gets called for enabled or disabled |
| planes. At best this seems to confuse drivers, worst it means they blow up |
| when the plane is disabled without the CRTC. The only special handling is |
| resetting values in the plane state structures, which instead should be moved |
| into the drm_plane_funcs->atomic_duplicate_state functions. |
| |
| - Once that's done, helpers could stop calling ->atomic_check for disabled |
| planes. |
| |
| - Then we could go through all the drivers and remove the more-or-less confused |
| checks for plane_state->fb and plane_state->crtc. |
| |
| Contact: Simona Vetter |
| |
| Level: Advanced |
| |
| Convert early atomic drivers to async commit helpers |
| ---------------------------------------------------- |
| |
| For the first year the atomic modeset helpers didn't support asynchronous / |
| nonblocking commits, and every driver had to hand-roll them. This is fixed |
| now, but there's still a pile of existing drivers that easily could be |
| converted over to the new infrastructure. |
| |
| One issue with the helpers is that they require that drivers handle completion |
| events for atomic commits correctly. But fixing these bugs is good anyway. |
| |
| Somewhat related is the legacy_cursor_update hack, which should be replaced with |
| the new atomic_async_check/commit functionality in the helpers in drivers that |
| still look at that flag. |
| |
| Contact: Simona Vetter, respective driver maintainers |
| |
| Level: Advanced |
| |
| Rename drm_atomic_state |
| ----------------------- |
| |
| The KMS framework uses two slightly different definitions for the ``state`` |
| concept. For a given object (plane, CRTC, encoder, etc., so |
| ``drm_$OBJECT_state``), the state is the entire state of that object. However, |
| at the device level, ``drm_atomic_state`` refers to a state update for a |
| limited number of objects. |
| |
| The state isn't the entire device state, but only the full state of some |
| objects in that device. This is confusing to newcomers, and |
| ``drm_atomic_state`` should be renamed to something clearer like |
| ``drm_atomic_commit``. |
| |
| In addition to renaming the structure itself, it would also imply renaming some |
| related functions (``drm_atomic_state_alloc``, ``drm_atomic_state_get``, |
| ``drm_atomic_state_put``, ``drm_atomic_state_init``, |
| ``__drm_atomic_state_free``, etc.). |
| |
| Contact: Maxime Ripard <mripard@kernel.org> |
| |
| Level: Advanced |
| |
| Fallout from atomic KMS |
| ----------------------- |
| |
| ``drm_atomic_helper.c`` provides a batch of functions which implement legacy |
| IOCTLs on top of the new atomic driver interface. Which is really nice for |
| gradual conversion of drivers, but unfortunately the semantic mismatches are |
| a bit too severe. So there's some follow-up work to adjust the function |
| interfaces to fix these issues: |
| |
| * atomic needs the lock acquire context. At the moment that's passed around |
| implicitly with some horrible hacks, and it's also allocate with |
| ``GFP_NOFAIL`` behind the scenes. All legacy paths need to start allocating |
| the acquire context explicitly on stack and then also pass it down into |
| drivers explicitly so that the legacy-on-atomic functions can use them. |
| |
| Except for some driver code this is done. This task should be finished by |
| adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all(). |
| |
| * A bunch of the vtable hooks are now in the wrong place: DRM has a split |
| between core vfunc tables (named ``drm_foo_funcs``), which are used to |
| implement the userspace ABI. And then there's the optional hooks for the |
| helper libraries (name ``drm_foo_helper_funcs``), which are purely for |
| internal use. Some of these hooks should be move from ``_funcs`` to |
| ``_helper_funcs`` since they are not part of the core ABI. There's a |
| ``FIXME`` comment in the kerneldoc for each such case in ``drm_crtc.h``. |
| |
| Contact: Simona Vetter |
| |
| Level: Intermediate |
| |
| Get rid of dev->struct_mutex from GEM drivers |
| --------------------------------------------- |
| |
| ``dev->struct_mutex`` is the Big DRM Lock from legacy days and infested |
| everything. Nowadays in modern drivers the only bit where it's mandatory is |
| serializing GEM buffer object destruction. Which unfortunately means drivers |
| have to keep track of that lock and either call ``unreference`` or |
| ``unreference_locked`` depending upon context. |
| |
| Core GEM doesn't have a need for ``struct_mutex`` any more since kernel 4.8, |
| and there's a GEM object ``free`` callback for any drivers which are |
| entirely ``struct_mutex`` free. |
| |
| For drivers that need ``struct_mutex`` it should be replaced with a driver- |
| private lock. The tricky part is the BO free functions, since those can't |
| reliably take that lock any more. Instead state needs to be protected with |
| suitable subordinate locks or some cleanup work pushed to a worker thread. For |
| performance-critical drivers it might also be better to go with a more |
| fine-grained per-buffer object and per-context lockings scheme. Currently only |
| the ``msm`` and `i915` drivers use ``struct_mutex``. |
| |
| Contact: Simona Vetter, respective driver maintainers |
| |
| Level: Advanced |
| |
| Move Buffer Object Locking to dma_resv_lock() |
| --------------------------------------------- |
| |
| Many drivers have their own per-object locking scheme, usually using |
| mutex_lock(). This causes all kinds of trouble for buffer sharing, since |
| depending which driver is the exporter and importer, the locking hierarchy is |
| reversed. |
| |
| To solve this we need one standard per-object locking mechanism, which is |
| dma_resv_lock(). This lock needs to be called as the outermost lock, with all |
| other driver specific per-object locks removed. The problem is that rolling out |
| the actual change to the locking contract is a flag day, due to struct dma_buf |
| buffer sharing. |
| |
| Level: Expert |
| |
| Convert logging to drm_* functions with drm_device parameter |
| ------------------------------------------------------------ |
| |
| For drivers which could have multiple instances, it is necessary to |
| differentiate between which is which in the logs. Since DRM_INFO/WARN/ERROR |
| don't do this, drivers used dev_info/warn/err to make this differentiation. We |
| now have drm_* variants of the drm print functions, so we can start to convert |
| those drivers back to using drm-formatted specific log messages. |
| |
| Before you start this conversion please contact the relevant maintainers to make |
| sure your work will be merged - not everyone agrees that the DRM dmesg macros |
| are better. |
| |
| Contact: Sean Paul, Maintainer of the driver you plan to convert |
| |
| Level: Starter |
| |
| Convert drivers to use simple modeset suspend/resume |
| ---------------------------------------------------- |
| |
| Most drivers (except i915 and nouveau) that use |
| drm_atomic_helper_suspend/resume() can probably be converted to use |
| drm_mode_config_helper_suspend/resume(). Also there's still open-coded version |
| of the atomic suspend/resume code in older atomic modeset drivers. |
| |
| Contact: Maintainer of the driver you plan to convert |
| |
| Level: Intermediate |
| |
| Reimplement functions in drm_fbdev_fb_ops without fbdev |
| ------------------------------------------------------- |
| |
| A number of callback functions in drm_fbdev_fb_ops could benefit from |
| being rewritten without dependencies on the fbdev module. Some of the |
| helpers could further benefit from using struct iosys_map instead of |
| raw pointers. |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de>, Simona Vetter |
| |
| Level: Advanced |
| |
| Benchmark and optimize blitting and format-conversion function |
| -------------------------------------------------------------- |
| |
| Drawing to display memory quickly is crucial for many applications' |
| performance. |
| |
| On at least x86-64, sys_imageblit() is significantly slower than |
| cfb_imageblit(), even though both use the same blitting algorithm and |
| the latter is written for I/O memory. It turns out that cfb_imageblit() |
| uses movl instructions, while sys_imageblit apparently does not. This |
| seems to be a problem with gcc's optimizer. DRM's format-conversion |
| helpers might be subject to similar issues. |
| |
| Benchmark and optimize fbdev's sys_() helpers and DRM's format-conversion |
| helpers. In cases that can be further optimized, maybe implement a different |
| algorithm. For micro-optimizations, use movl/movq instructions explicitly. |
| That might possibly require architecture-specific helpers (e.g., storel() |
| storeq()). |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de> |
| |
| Level: Intermediate |
| |
| drm_framebuffer_funcs and drm_mode_config_funcs.fb_create cleanup |
| ----------------------------------------------------------------- |
| |
| A lot more drivers could be switched over to the drm_gem_framebuffer helpers. |
| Various hold-ups: |
| |
| - Need to switch over to the generic dirty tracking code using |
| drm_atomic_helper_dirtyfb first (e.g. qxl). |
| |
| - Need to switch to drm_fbdev_generic_setup(), otherwise a lot of the custom fb |
| setup code can't be deleted. |
| |
| - Need to switch to drm_gem_fb_create(), as now drm_gem_fb_create() checks for |
| valid formats for atomic drivers. |
| |
| - Many drivers subclass drm_framebuffer, we'd need a embedding compatible |
| version of the varios drm_gem_fb_create functions. Maybe called |
| drm_gem_fb_create/_with_dirty/_with_funcs as needed. |
| |
| Contact: Simona Vetter |
| |
| Level: Intermediate |
| |
| Generic fbdev defio support |
| --------------------------- |
| |
| The defio support code in the fbdev core has some very specific requirements, |
| which means drivers need to have a special framebuffer for fbdev. The main |
| issue is that it uses some fields in struct page itself, which breaks shmem |
| gem objects (and other things). To support defio, affected drivers require |
| the use of a shadow buffer, which may add CPU and memory overhead. |
| |
| Possible solution would be to write our own defio mmap code in the drm fbdev |
| emulation. It would need to fully wrap the existing mmap ops, forwarding |
| everything after it has done the write-protect/mkwrite trickery: |
| |
| - In the drm_fbdev_fb_mmap helper, if we need defio, change the |
| default page prots to write-protected with something like this:: |
| |
| vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); |
| |
| - Set the mkwrite and fsync callbacks with similar implementions to the core |
| fbdev defio stuff. These should all work on plain ptes, they don't actually |
| require a struct page. uff. These should all work on plain ptes, they don't |
| actually require a struct page. |
| |
| - Track the dirty pages in a separate structure (bitfield with one bit per page |
| should work) to avoid clobbering struct page. |
| |
| Might be good to also have some igt testcases for this. |
| |
| Contact: Simona Vetter, Noralf Tronnes |
| |
| Level: Advanced |
| |
| connector register/unregister fixes |
| ----------------------------------- |
| |
| - For most connectors it's a no-op to call drm_connector_register/unregister |
| directly from driver code, drm_dev_register/unregister take care of this |
| already. We can remove all of them. |
| |
| - For dp drivers it's a bit more a mess, since we need the connector to be |
| registered when calling drm_dp_aux_register. Fix this by instead calling |
| drm_dp_aux_init, and moving the actual registering into a late_register |
| callback as recommended in the kerneldoc. |
| |
| Level: Intermediate |
| |
| Remove load/unload callbacks |
| ---------------------------- |
| |
| The load/unload callbacks in struct &drm_driver are very much midlayers, plus |
| for historical reasons they get the ordering wrong (and we can't fix that) |
| between setting up the &drm_driver structure and calling drm_dev_register(). |
| |
| - Rework drivers to no longer use the load/unload callbacks, directly coding the |
| load/unload sequence into the driver's probe function. |
| |
| - Once all drivers are converted, remove the load/unload callbacks. |
| |
| Contact: Simona Vetter |
| |
| Level: Intermediate |
| |
| Replace drm_detect_hdmi_monitor() with drm_display_info.is_hdmi |
| --------------------------------------------------------------- |
| |
| Once EDID is parsed, the monitor HDMI support information is available through |
| drm_display_info.is_hdmi. Many drivers still call drm_detect_hdmi_monitor() to |
| retrieve the same information, which is less efficient. |
| |
| Audit each individual driver calling drm_detect_hdmi_monitor() and switch to |
| drm_display_info.is_hdmi if applicable. |
| |
| Contact: Laurent Pinchart, respective driver maintainers |
| |
| Level: Intermediate |
| |
| Consolidate custom driver modeset properties |
| -------------------------------------------- |
| |
| Before atomic modeset took place, many drivers where creating their own |
| properties. Among other things, atomic brought the requirement that custom, |
| driver specific properties should not be used. |
| |
| For this task, we aim to introduce core helpers or reuse the existing ones |
| if available: |
| |
| A quick, unconfirmed, examples list. |
| |
| Introduce core helpers: |
| - audio (amdgpu, intel, gma500, radeon) |
| - brightness, contrast, etc (armada, nouveau) - overlay only (?) |
| - broadcast rgb (gma500, intel) |
| - colorkey (armada, nouveau, rcar) - overlay only (?) |
| - dither (amdgpu, nouveau, radeon) - varies across drivers |
| - underscan family (amdgpu, radeon, nouveau) |
| |
| Already in core: |
| - colorspace (sti) |
| - tv format names, enhancements (gma500, intel) |
| - tv overscan, margins, etc. (gma500, intel) |
| - zorder (omapdrm) - same as zpos (?) |
| |
| |
| Contact: Emil Velikov, respective driver maintainers |
| |
| Level: Intermediate |
| |
| Use struct iosys_map throughout codebase |
| ---------------------------------------- |
| |
| Pointers to shared device memory are stored in struct iosys_map. Each |
| instance knows whether it refers to system or I/O memory. Most of the DRM-wide |
| interface have been converted to use struct iosys_map, but implementations |
| often still use raw pointers. |
| |
| The task is to use struct iosys_map where it makes sense. |
| |
| * Memory managers should use struct iosys_map for dma-buf-imported buffers. |
| * TTM might benefit from using struct iosys_map internally. |
| * Framebuffer copying and blitting helpers should operate on struct iosys_map. |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de>, Christian König, Simona Vetter |
| |
| Level: Intermediate |
| |
| Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly |
| -------------------------------------------------------------------------------------- |
| |
| The values in struct drm_mode_config.{max_width,max_height} describe the |
| maximum supported framebuffer size. It's the virtual screen size, but many |
| drivers treat it like limitations of the physical resolution. |
| |
| The maximum width depends on the hardware's maximum scanline pitch. The |
| maximum height depends on the amount of addressable video memory. Review all |
| drivers to initialize the fields to the correct values. |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de> |
| |
| Level: Intermediate |
| |
| Request memory regions in all drivers |
| ------------------------------------- |
| |
| Go through all drivers and add code to request the memory regions that the |
| driver uses. This requires adding calls to request_mem_region(), |
| pci_request_region() or similar functions. Use helpers for managed cleanup |
| where possible. |
| |
| Drivers are pretty bad at doing this and there used to be conflicts among |
| DRM and fbdev drivers. Still, it's the correct thing to do. |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de> |
| |
| Level: Starter |
| |
| Remove driver dependencies on FB_DEVICE |
| --------------------------------------- |
| |
| A number of fbdev drivers provide attributes via sysfs and therefore depend |
| on CONFIG_FB_DEVICE to be selected. Review each driver and attempt to make |
| any dependencies on CONFIG_FB_DEVICE optional. At the minimum, the respective |
| code in the driver could be conditionalized via ifdef CONFIG_FB_DEVICE. Not |
| all drivers might be able to drop CONFIG_FB_DEVICE. |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de> |
| |
| Level: Starter |
| |
| Remove disable/unprepare in remove/shutdown in panel-simple and panel-edp |
| ------------------------------------------------------------------------- |
| |
| As of commit d2aacaf07395 ("drm/panel: Check for already prepared/enabled in |
| drm_panel"), we have a check in the drm_panel core to make sure nobody |
| double-calls prepare/enable/disable/unprepare. Eventually that should probably |
| be turned into a WARN_ON() or somehow made louder. |
| |
| At the moment, we expect that we may still encounter the warnings in the |
| drm_panel core when using panel-simple and panel-edp. Since those panel |
| drivers are used with a lot of different DRM modeset drivers they still |
| make an extra effort to disable/unprepare the panel themsevles at shutdown |
| time. Specifically we could still encounter those warnings if the panel |
| driver gets shutdown() _before_ the DRM modeset driver and the DRM modeset |
| driver properly calls drm_atomic_helper_shutdown() in its own shutdown() |
| callback. Warnings could be avoided in such a case by using something like |
| device links to ensure that the panel gets shutdown() after the DRM modeset |
| driver. |
| |
| Once all DRM modeset drivers are known to shutdown properly, the extra |
| calls to disable/unprepare in remove/shutdown in panel-simple and panel-edp |
| should be removed and this TODO item marked complete. |
| |
| Contact: Douglas Anderson <dianders@chromium.org> |
| |
| Level: Intermediate |
| |
| Transition away from using mipi_dsi_*_write_seq() |
| ------------------------------------------------- |
| |
| The macros mipi_dsi_generic_write_seq() and mipi_dsi_dcs_write_seq() are |
| non-intuitive because, if there are errors, they return out of the *caller's* |
| function. We should move all callers to use mipi_dsi_generic_write_seq_multi() |
| and mipi_dsi_dcs_write_seq_multi() macros instead. |
| |
| Once all callers are transitioned, the macros and the functions that they call, |
| mipi_dsi_generic_write_chatty() and mipi_dsi_dcs_write_buffer_chatty(), can |
| probably be removed. Alternatively, if people feel like the _multi() variants |
| are overkill for some use cases, we could keep the mipi_dsi_*_write_seq() |
| variants but change them not to return out of the caller. |
| |
| Contact: Douglas Anderson <dianders@chromium.org> |
| |
| Level: Starter |
| |
| |
| Core refactorings |
| ================= |
| |
| Make panic handling work |
| ------------------------ |
| |
| This is a really varied tasks with lots of little bits and pieces: |
| |
| * The panic path can't be tested currently, leading to constant breaking. The |
| main issue here is that panics can be triggered from hardirq contexts and |
| hence all panic related callback can run in hardirq context. It would be |
| awesome if we could test at least the fbdev helper code and driver code by |
| e.g. trigger calls through drm debugfs files. hardirq context could be |
| achieved by using an IPI to the local processor. |
| |
| * There's a massive confusion of different panic handlers. DRM fbdev emulation |
| helpers had their own (long removed), but on top of that the fbcon code itself |
| also has one. We need to make sure that they stop fighting over each other. |
| This is worked around by checking ``oops_in_progress`` at various entry points |
| into the DRM fbdev emulation helpers. A much cleaner approach here would be to |
| switch fbcon to the `threaded printk support |
| <https://lwn.net/Articles/800946/>`_. |
| |
| * ``drm_can_sleep()`` is a mess. It hides real bugs in normal operations and |
| isn't a full solution for panic paths. We need to make sure that it only |
| returns true if there's a panic going on for real, and fix up all the |
| fallout. |
| |
| * The panic handler must never sleep, which also means it can't ever |
| ``mutex_lock()``. Also it can't grab any other lock unconditionally, not |
| even spinlocks (because NMI and hardirq can panic too). We need to either |
| make sure to not call such paths, or trylock everything. Really tricky. |
| |
| * A clean solution would be an entirely separate panic output support in KMS, |
| bypassing the current fbcon support. See `[PATCH v2 0/3] drm: Add panic handling |
| <https://lore.kernel.org/dri-devel/20190311174218.51899-1-noralf@tronnes.org/>`_. |
| |
| * Encoding the actual oops and preceding dmesg in a QR might help with the |
| dread "important stuff scrolled away" problem. See `[RFC][PATCH] Oops messages |
| transfer using QR codes |
| <https://lore.kernel.org/lkml/1446217392-11981-1-git-send-email-alexandru.murtaza@intel.com/>`_ |
| for some example code that could be reused. |
| |
| Contact: Simona Vetter |
| |
| Level: Advanced |
| |
| Clean up the debugfs support |
| ---------------------------- |
| |
| There's a bunch of issues with it: |
| |
| - Convert drivers to support the drm_debugfs_add_files() function instead of |
| the drm_debugfs_create_files() function. |
| |
| - Improve late-register debugfs by rolling out the same debugfs pre-register |
| infrastructure for connector and crtc too. That way, the drivers won't need to |
| split their setup code into init and register anymore. |
| |
| - We probably want to have some support for debugfs files on crtc/connectors and |
| maybe other kms objects directly in core. There's even drm_print support in |
| the funcs for these objects to dump kms state, so it's all there. And then the |
| ->show() functions should obviously give you a pointer to the right object. |
| |
| - The drm_driver->debugfs_init hooks we have is just an artifact of the old |
| midlayered load sequence. DRM debugfs should work more like sysfs, where you |
| can create properties/files for an object anytime you want, and the core |
| takes care of publishing/unpuplishing all the files at register/unregister |
| time. Drivers shouldn't need to worry about these technicalities, and fixing |
| this (together with the drm_minor->drm_device move) would allow us to remove |
| debugfs_init. |
| |
| Contact: Simona Vetter |
| |
| Level: Intermediate |
| |
| Object lifetime fixes |
| --------------------- |
| |
| There's two related issues here |
| |
| - Cleanup up the various ->destroy callbacks, which often are all the same |
| simple code. |
| |
| - Lots of drivers erroneously allocate DRM modeset objects using devm_kzalloc, |
| which results in use-after free issues on driver unload. This can be serious |
| trouble even for drivers for hardware integrated on the SoC due to |
| EPROBE_DEFERRED backoff. |
| |
| Both these problems can be solved by switching over to drmm_kzalloc(), and the |
| various convenience wrappers provided, e.g. drmm_crtc_alloc_with_planes(), |
| drmm_universal_plane_alloc(), ... and so on. |
| |
| Contact: Simona Vetter |
| |
| Level: Intermediate |
| |
| Remove automatic page mapping from dma-buf importing |
| ---------------------------------------------------- |
| |
| When importing dma-bufs, the dma-buf and PRIME frameworks automatically map |
| imported pages into the importer's DMA area. drm_gem_prime_fd_to_handle() and |
| drm_gem_prime_handle_to_fd() require that importers call dma_buf_attach() |
| even if they never do actual device DMA, but only CPU access through |
| dma_buf_vmap(). This is a problem for USB devices, which do not support DMA |
| operations. |
| |
| To fix the issue, automatic page mappings should be removed from the |
| buffer-sharing code. Fixing this is a bit more involved, since the import/export |
| cache is also tied to &drm_gem_object.import_attach. Meanwhile we paper over |
| this problem for USB devices by fishing out the USB host controller device, as |
| long as that supports DMA. Otherwise importing can still needlessly fail. |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de>, Simona Vetter |
| |
| Level: Advanced |
| |
| |
| Better Testing |
| ============== |
| |
| Add unit tests using the Kernel Unit Testing (KUnit) framework |
| -------------------------------------------------------------- |
| |
| The `KUnit <https://www.kernel.org/doc/html/latest/dev-tools/kunit/index.html>`_ |
| provides a common framework for unit tests within the Linux kernel. Having a |
| test suite would allow to identify regressions earlier. |
| |
| A good candidate for the first unit tests are the format-conversion helpers in |
| ``drm_format_helper.c``. |
| |
| Contact: Javier Martinez Canillas <javierm@redhat.com> |
| |
| Level: Intermediate |
| |
| Clean up and document former selftests suites |
| --------------------------------------------- |
| |
| Some KUnit test suites (drm_buddy, drm_cmdline_parser, drm_damage_helper, |
| drm_format, drm_framebuffer, drm_dp_mst_helper, drm_mm, drm_plane_helper and |
| drm_rect) are former selftests suites that have been converted over when KUnit |
| was first introduced. |
| |
| These suites were fairly undocumented, and with different goals than what unit |
| tests can be. Trying to identify what each test in these suites actually test |
| for, whether that makes sense for a unit test, and either remove it if it |
| doesn't or document it if it does would be of great help. |
| |
| Contact: Maxime Ripard <mripard@kernel.org> |
| |
| Level: Intermediate |
| |
| Enable trinity for DRM |
| ---------------------- |
| |
| And fix up the fallout. Should be really interesting ... |
| |
| Level: Advanced |
| |
| Make KMS tests in i-g-t generic |
| ------------------------------- |
| |
| The i915 driver team maintains an extensive testsuite for the i915 DRM driver, |
| including tons of testcases for corner-cases in the modesetting API. It would |
| be awesome if those tests (at least the ones not relying on Intel-specific GEM |
| features) could be made to run on any KMS driver. |
| |
| Basic work to run i-g-t tests on non-i915 is done, what's now missing is mass- |
| converting things over. For modeset tests we also first need a bit of |
| infrastructure to use dumb buffers for untiled buffers, to be able to run all |
| the non-i915 specific modeset tests. |
| |
| Level: Advanced |
| |
| Extend virtual test driver (VKMS) |
| --------------------------------- |
| |
| See the documentation of :ref:`VKMS <vkms>` for more details. This is an ideal |
| internship task, since it only requires a virtual machine and can be sized to |
| fit the available time. |
| |
| Level: See details |
| |
| Backlight Refactoring |
| --------------------- |
| |
| Backlight drivers have a triple enable/disable state, which is a bit overkill. |
| Plan to fix this: |
| |
| 1. Roll out backlight_enable() and backlight_disable() helpers everywhere. This |
| has started already. |
| 2. In all, only look at one of the three status bits set by the above helpers. |
| 3. Remove the other two status bits. |
| |
| Contact: Simona Vetter |
| |
| Level: Intermediate |
| |
| Driver Specific |
| =============== |
| |
| AMD DC Display Driver |
| --------------------- |
| |
| AMD DC is the display driver for AMD devices starting with Vega. There has been |
| a bunch of progress cleaning it up but there's still plenty of work to be done. |
| |
| See drivers/gpu/drm/amd/display/TODO for tasks. |
| |
| Contact: Harry Wentland, Alex Deucher |
| |
| Bootsplash |
| ========== |
| |
| There is support in place now for writing internal DRM clients making it |
| possible to pick up the bootsplash work that was rejected because it was written |
| for fbdev. |
| |
| - [v6,8/8] drm/client: Hack: Add bootsplash example |
| https://patchwork.freedesktop.org/patch/306579/ |
| |
| - [RFC PATCH v2 00/13] Kernel based bootsplash |
| https://lore.kernel.org/r/20171213194755.3409-1-mstaudt@suse.de |
| |
| Contact: Sam Ravnborg |
| |
| Level: Advanced |
| |
| Brightness handling on devices with multiple internal panels |
| ============================================================ |
| |
| On x86/ACPI devices there can be multiple backlight firmware interfaces: |
| (ACPI) video, vendor specific and others. As well as direct/native (PWM) |
| register programming by the KMS driver. |
| |
| To deal with this backlight drivers used on x86/ACPI call |
| acpi_video_get_backlight_type() which has heuristics (+quirks) to select |
| which backlight interface to use; and backlight drivers which do not match |
| the returned type will not register themselves, so that only one backlight |
| device gets registered (in a single GPU setup, see below). |
| |
| At the moment this more or less assumes that there will only |
| be 1 (internal) panel on a system. |
| |
| On systems with 2 panels this may be a problem, depending on |
| what interface acpi_video_get_backlight_type() selects: |
| |
| 1. native: in this case the KMS driver is expected to know which backlight |
| device belongs to which output so everything should just work. |
| 2. video: this does support controlling multiple backlights, but some work |
| will need to be done to get the output <-> backlight device mapping |
| |
| The above assumes both panels will require the same backlight interface type. |
| Things will break on systems with multiple panels where the 2 panels need |
| a different type of control. E.g. one panel needs ACPI video backlight control, |
| where as the other is using native backlight control. Currently in this case |
| only one of the 2 required backlight devices will get registered, based on |
| the acpi_video_get_backlight_type() return value. |
| |
| If this (theoretical) case ever shows up, then supporting this will need some |
| work. A possible solution here would be to pass a device and connector-name |
| to acpi_video_get_backlight_type() so that it can deal with this. |
| |
| Note in a way we already have a case where userspace sees 2 panels, |
| in dual GPU laptop setups with a mux. On those systems we may see |
| either 2 native backlight devices; or 2 native backlight devices. |
| |
| Userspace already has code to deal with this by detecting if the related |
| panel is active (iow which way the mux between the GPU and the panels |
| points) and then uses that backlight device. Userspace here very much |
| assumes a single panel though. It picks only 1 of the 2 backlight devices |
| and then only uses that one. |
| |
| Note that all userspace code (that I know off) is currently hardcoded |
| to assume a single panel. |
| |
| Before the recent changes to not register multiple (e.g. video + native) |
| /sys/class/backlight devices for a single panel (on a single GPU laptop), |
| userspace would see multiple backlight devices all controlling the same |
| backlight. |
| |
| To deal with this userspace had to always picks one preferred device under |
| /sys/class/backlight and will ignore the others. So to support brightness |
| control on multiple panels userspace will need to be updated too. |
| |
| There are plans to allow brightness control through the KMS API by adding |
| a "display brightness" property to drm_connector objects for panels. This |
| solves a number of issues with the /sys/class/backlight API, including not |
| being able to map a sysfs backlight device to a specific connector. Any |
| userspace changes to add support for brightness control on devices with |
| multiple panels really should build on top of this new KMS property. |
| |
| Contact: Hans de Goede |
| |
| Level: Advanced |
| |
| Buffer age or other damage accumulation algorithm for buffer damage |
| =================================================================== |
| |
| Drivers that do per-buffer uploads, need a buffer damage handling (rather than |
| frame damage like drivers that do per-plane or per-CRTC uploads), but there is |
| no support to get the buffer age or any other damage accumulation algorithm. |
| |
| For this reason, the damage helpers just fallback to a full plane update if the |
| framebuffer attached to a plane has changed since the last page-flip. Drivers |
| set &drm_plane_state.ignore_damage_clips to true as indication to |
| drm_atomic_helper_damage_iter_init() and drm_atomic_helper_damage_iter_next() |
| helpers that the damage clips should be ignored. |
| |
| This should be improved to get damage tracking properly working on drivers that |
| do per-buffer uploads. |
| |
| More information about damage tracking and references to learning materials can |
| be found in :ref:`damage_tracking_properties`. |
| |
| Contact: Javier Martinez Canillas <javierm@redhat.com> |
| |
| Level: Advanced |
| |
| Outside DRM |
| =========== |
| |
| Convert fbdev drivers to DRM |
| ---------------------------- |
| |
| There are plenty of fbdev drivers for older hardware. Some hardware has |
| become obsolete, but some still provides good(-enough) framebuffers. The |
| drivers that are still useful should be converted to DRM and afterwards |
| removed from fbdev. |
| |
| Very simple fbdev drivers can best be converted by starting with a new |
| DRM driver. Simple KMS helpers and SHMEM should be able to handle any |
| existing hardware. The new driver's call-back functions are filled from |
| existing fbdev code. |
| |
| More complex fbdev drivers can be refactored step-by-step into a DRM |
| driver with the help of the DRM fbconv helpers [4]_. These helpers provide |
| the transition layer between the DRM core infrastructure and the fbdev |
| driver interface. Create a new DRM driver on top of the fbconv helpers, |
| copy over the fbdev driver, and hook it up to the DRM code. Examples for |
| several fbdev drivers are available in Thomas Zimmermann's fbconv tree |
| [4]_, as well as a tutorial of this process [5]_. The result is a primitive |
| DRM driver that can run X11 and Weston. |
| |
| .. [4] https://gitlab.freedesktop.org/tzimmermann/linux/tree/fbconv |
| .. [5] https://gitlab.freedesktop.org/tzimmermann/linux/blob/fbconv/drivers/gpu/drm/drm_fbconv_helper.c |
| |
| Contact: Thomas Zimmermann <tzimmermann@suse.de> |
| |
| Level: Advanced |
