drm/i915: Use PM QoS to prevent C-State starvation of gen3 GPU

945 class hardware has an interesting quirk in which the vblank
interrupt is not raised if the CPU is in a low power state. (We also
suspect that the memory bus is clocked to the CPU/c-state and not the
GPU so there are secondary starvation issues.) In order to prevent the
most obvious issue of the low of the vblank interrupt (stuttering
compositing that only updates when the mouse is moving) is to install a
PM QoS request to prevent low c-states whilst the GPU is active.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 536368a43412..9b9a771110a4 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -35,6 +35,7 @@
 #include "intel_ringbuffer.h"
 #include <linux/io-mapping.h>
 #include <linux/i2c.h>
+#include <linux/pm_qos_params.h>
 #include <drm/intel-gtt.h>
 
 /* General customization:
@@ -310,6 +311,10 @@ typedef struct drm_i915_private {
         int vblank_pipe;
         int num_pipe;
 
+        atomic_t vblank_enabled;
+        struct pm_qos_request_list vblank_pm_qos;
+        struct work_struct vblank_work;
+
         /* For hangcheck timer */
 #define DRM_I915_HANGCHECK_PERIOD 1500 /* in ms */
         struct timer_list hangcheck_timer;