drm/i915: Implement a better i945gm vblank irq vs. C-states workaround
The current "disable C3+" workaround for the delayed vblank
irqs on i945gm no longer works. I'm not sure what changed, but
now I need to also disable C2. I also got my hands on a i915gm
machine that suffers from the same issue.
After some furious poking of registers I managed to find a
better workaround: The "Do not Turn off Core Render Clock in C
states" bit. With that I no longer have to disable any C-states,
and as a nice bonus the power cost is only ~1/4 of the
"disable C3+" method (which mind you doesn't even work anymore,
and so would have an even higher power cost if we made it work
by also disabling C2).
So let's throw out all the cpuidle/qos crap and just toggle
the magic bit as needed. And we extend the workaround to cover
i915gm as well.
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191003140231.24408-1-ville.syrjala@linux.intel.com
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 813ddea..6d67bd2 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -2709,6 +2709,7 @@ static inline bool i915_mmio_reg_valid(i915_reg_t reg)
#define VLV_GU_CTL0 _MMIO(VLV_DISPLAY_BASE + 0x2030)
#define VLV_GU_CTL1 _MMIO(VLV_DISPLAY_BASE + 0x2034)
#define SCPD0 _MMIO(0x209c) /* 915+ only */
+#define CSTATE_RENDER_CLOCK_GATE_DISABLE (1 << 5)
#define GEN2_IER _MMIO(0x20a0)
#define GEN2_IIR _MMIO(0x20a4)
#define GEN2_IMR _MMIO(0x20a8)
