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// SPDX-License-Identifier: MIT
* Copyright (C) 2019 Google, Inc.
* Authors:
* Sean Paul <>
#include <linux/average.h>
#include <linux/bitops.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <drm/drm_atomic.h>
#include <drm/drm_atomic_helper.h>
#include <drm/drm_connector.h>
#include <drm/drm_crtc.h>
#include <drm/drm_device.h>
#include <drm/drm_mode_config.h>
#include <drm/drm_modeset_lock.h>
#include <drm/drm_print.h>
#include <drm/drm_self_refresh_helper.h>
* DOC: overview
* This helper library provides an easy way for drivers to leverage the atomic
* framework to implement panel self refresh (SR) support. Drivers are
* responsible for initializing and cleaning up the SR helpers on load/unload
* (see &drm_self_refresh_helper_init/&drm_self_refresh_helper_cleanup).
* The connector is responsible for setting
* &drm_connector_state.self_refresh_aware to true at runtime if it is SR-aware
* (meaning it knows how to initiate self refresh on the panel).
* Once a crtc has enabled SR using &drm_self_refresh_helper_init, the
* helpers will monitor activity and call back into the driver to enable/disable
* SR as appropriate. The best way to think about this is that it's a DPMS
* on/off request with &drm_crtc_state.self_refresh_active set in crtc state
* that tells you to disable/enable SR on the panel instead of power-cycling it.
* During SR, drivers may choose to fully disable their crtc/encoder/bridge
* hardware (in which case no driver changes are necessary), or they can inspect
* &drm_crtc_state.self_refresh_active if they want to enter low power mode
* without full disable (in case full disable/enable is too slow).
* SR will be deactivated if there are any atomic updates affecting the
* pipe that is in SR mode. If a crtc is driving multiple connectors, all
* connectors must be SR aware and all will enter/exit SR mode at the same time.
* If the crtc and connector are SR aware, but the panel connected does not
* support it (or is otherwise unable to enter SR), the driver should fail
* atomic_check when &drm_crtc_state.self_refresh_active is true.
DECLARE_EWMA(psr_time, 4, 4)
struct drm_self_refresh_data {
struct drm_crtc *crtc;
struct delayed_work entry_work;
struct mutex avg_mutex;
struct ewma_psr_time entry_avg_ms;
struct ewma_psr_time exit_avg_ms;
static void drm_self_refresh_helper_entry_work(struct work_struct *work)
struct drm_self_refresh_data *sr_data = container_of(
struct drm_self_refresh_data, entry_work);
struct drm_crtc *crtc = sr_data->crtc;
struct drm_device *dev = crtc->dev;
struct drm_modeset_acquire_ctx ctx;
struct drm_atomic_state *state;
struct drm_connector *conn;
struct drm_connector_state *conn_state;
struct drm_crtc_state *crtc_state;
int i, ret = 0;
drm_modeset_acquire_init(&ctx, 0);
state = drm_atomic_state_alloc(dev);
if (!state) {
ret = -ENOMEM;
goto out_drop_locks;
state->acquire_ctx = &ctx;
crtc_state = drm_atomic_get_crtc_state(state, crtc);
if (IS_ERR(crtc_state)) {
ret = PTR_ERR(crtc_state);
goto out;
if (!crtc_state->enable)
goto out;
ret = drm_atomic_add_affected_connectors(state, crtc);
if (ret)
goto out;
for_each_new_connector_in_state(state, conn, conn_state, i) {
if (!conn_state->self_refresh_aware)
goto out;
crtc_state->active = false;
crtc_state->self_refresh_active = true;
ret = drm_atomic_commit(state);
if (ret)
goto out;
if (ret == -EDEADLK) {
ret = drm_modeset_backoff(&ctx);
if (!ret)
goto retry;
* drm_self_refresh_helper_update_avg_times - Updates a crtc's SR time averages
* @state: the state which has just been applied to hardware
* @commit_time_ms: the amount of time in ms that this commit took to complete
* @new_self_refresh_mask: bitmask of crtc's that have self_refresh_active in
* new state
* Called after &drm_mode_config_funcs.atomic_commit_tail, this function will
* update the average entry/exit self refresh times on self refresh transitions.
* These averages will be used when calculating how long to delay before
* entering self refresh mode after activity.
drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
unsigned int commit_time_ms,
unsigned int new_self_refresh_mask)
struct drm_crtc *crtc;
struct drm_crtc_state *old_crtc_state;
int i;
for_each_old_crtc_in_state(state, crtc, old_crtc_state, i) {
bool new_self_refresh_active = new_self_refresh_mask & BIT(i);
struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
struct ewma_psr_time *time;
if (old_crtc_state->self_refresh_active ==
if (new_self_refresh_active)
time = &sr_data->entry_avg_ms;
time = &sr_data->exit_avg_ms;
ewma_psr_time_add(time, commit_time_ms);
* drm_self_refresh_helper_alter_state - Alters the atomic state for SR exit
* @state: the state currently being checked
* Called at the end of atomic check. This function checks the state for flags
* incompatible with self refresh exit and changes them. This is a bit
* disingenuous since userspace is expecting one thing and we're giving it
* another. However in order to keep self refresh entirely hidden from
* userspace, this is required.
* At the end, we queue up the self refresh entry work so we can enter PSR after
* the desired delay.
void drm_self_refresh_helper_alter_state(struct drm_atomic_state *state)
struct drm_crtc *crtc;
struct drm_crtc_state *crtc_state;
int i;
if (state->async_update || !state->allow_modeset) {
for_each_old_crtc_in_state(state, crtc, crtc_state, i) {
if (crtc_state->self_refresh_active) {
state->async_update = false;
state->allow_modeset = true;
for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
struct drm_self_refresh_data *sr_data;
unsigned int delay;
/* Don't trigger the entry timer when we're already in SR */
if (crtc_state->self_refresh_active)
sr_data = crtc->self_refresh_data;
if (!sr_data)
delay = (ewma_psr_time_read(&sr_data->entry_avg_ms) +
ewma_psr_time_read(&sr_data->exit_avg_ms)) * 2;
mod_delayed_work(system_wq, &sr_data->entry_work,
* drm_self_refresh_helper_init - Initializes self refresh helpers for a crtc
* @crtc: the crtc which supports self refresh supported displays
* Returns zero if successful or -errno on failure
int drm_self_refresh_helper_init(struct drm_crtc *crtc)
struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
/* Helper is already initialized */
if (WARN_ON(sr_data))
return -EINVAL;
sr_data = kzalloc(sizeof(*sr_data), GFP_KERNEL);
if (!sr_data)
return -ENOMEM;
sr_data->crtc = crtc;
* Seed the averages so they're non-zero (and sufficiently large
* for even poorly performing panels). As time goes on, this will be
* averaged out and the values will trend to their true value.
ewma_psr_time_add(&sr_data->entry_avg_ms, SELF_REFRESH_AVG_SEED_MS);
ewma_psr_time_add(&sr_data->exit_avg_ms, SELF_REFRESH_AVG_SEED_MS);
crtc->self_refresh_data = sr_data;
return 0;
* drm_self_refresh_helper_cleanup - Cleans up self refresh helpers for a crtc
* @crtc: the crtc to cleanup
void drm_self_refresh_helper_cleanup(struct drm_crtc *crtc)
struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
/* Helper is already uninitialized */
if (!sr_data)
crtc->self_refresh_data = NULL;