From: Mark Yacoub <markyacoub@xxxxxxxxxx>
[why]
Reading frame count register used to get the vblank counter, which calls
dpu_encoder_phys to get the frame count. Even when it's disabled, the
vblank counter (through frame count) should return a valid value for the
count. An invalid value of 0, when compared to vblank->last (in
drm_vblank.c::drm_update_vblank_count()) returns an invalid number that
throws off the vblank counter for the lifetime of the process.
Rationale:
In drm_vblank.c::drm_update_vblank_count(), the new diff is calculated
through:
diff = (cur_vblank - vblank->last) & max_vblank_count;
cur_vblank comes from: cur_vblank = __get_vblank_counter(dev, pipe);
When the value is 0, diff results in a negative number (a very large
number as it's unsigned), which inflates the vblank count when the diff
is added to the current vblank->count.
[How]
Read frame_count register whether interface timing engine is enabled or
not.
Fixes: IGT:kms_flip::modeset-vs-vblank-race-interruptible
Tested on ChromeOS Trogdor(msm)
Signed-off-by: Mark Yacoub <markyacoub@xxxxxxxxxxxx>
---
drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c | 9 ++-------
drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h | 2 +-
2 files changed, 3 insertions(+), 8 deletions(-)
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
index 116e2b5b1a90f..c436d901629f3 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
@@ -266,13 +266,8 @@ static void dpu_hw_intf_get_status(
s->is_en = DPU_REG_READ(c, INTF_TIMING_ENGINE_EN);
s->is_prog_fetch_en = !!(DPU_REG_READ(c, INTF_CONFIG) & BIT(31));
- if (s->is_en) {
- s->frame_count = DPU_REG_READ(c, INTF_FRAME_COUNT);
- s->line_count = DPU_REG_READ(c, INTF_LINE_COUNT);
- } else {
- s->line_count = 0;
- s->frame_count = 0;
- }
+ s->frame_count = DPU_REG_READ(c, INTF_FRAME_COUNT);
+ s->line_count = DPU_REG_READ(c, INTF_LINE_COUNT);
}
static u32 dpu_hw_intf_get_line_count(struct dpu_hw_intf *intf)
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h
index 3568be80dab51..877ff48bfef04 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h
@@ -41,7 +41,7 @@ struct intf_prog_fetch {
struct intf_status {
u8 is_en; /* interface timing engine is enabled or not */
u8 is_prog_fetch_en; /* interface prog fetch counter is enabled or not */
- u32 frame_count; /* frame count since timing engine enabled */
+ u32 frame_count; /* frame count since timing engine first enabled */
u32 line_count; /* current line count including blanking */
};
--
2.33.0.rc1.237.g0d66db33f3-goog
