drm/msm: Change dpu_crtc_get_vblank_counter to use vsync count.

[why]
vsync_cnt atomic counter increments for every hw vsync. On the other
hand, frame count is a register that increments when the frame gets
actually pushed out. We cannnot read this register whenever the timing
engine is off, but vblank counter should still return a valid number.
This behavior also matches the downstream driver.

[How]
Read the encoder vsync count instead of the dpu_encoder_phys frame
count.

Suggested-by: Abhinav Kumar <abhinavk@codeaurora.org>
CC: Rob Clark <robdclark@chromium.org>
Signed-off-by: Mark Yacoub <markyacoub@chromium.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Link: https://lore.kernel.org/r/20210830181359.124267-1-markyacoub@chromium.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c

@@ -72,15 +72,13 @@ static struct drm_encoder *get_encoder_from_crtc(struct drm_crtc *crtc)
 
 static u32 dpu_crtc_get_vblank_counter(struct drm_crtc *crtc)
 {
-	struct drm_encoder *encoder;
-
-	encoder = get_encoder_from_crtc(crtc);
+	struct drm_encoder *encoder = get_encoder_from_crtc(crtc);
 	if (!encoder) {
 		DRM_ERROR("no encoder found for crtc %d\n", crtc->index);
-		return false;
+		return 0;
 	}
 
-	return dpu_encoder_get_frame_count(encoder);
+	return dpu_encoder_get_vsync_count(encoder);
 }
 
 static bool dpu_crtc_get_scanout_position(struct drm_crtc *crtc,

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c

@@ -395,19 +395,11 @@ int dpu_encoder_helper_unregister_irq(struct dpu_encoder_phys *phys_enc,
 	return 0;
 }
 
-int dpu_encoder_get_frame_count(struct drm_encoder *drm_enc)
+int dpu_encoder_get_vsync_count(struct drm_encoder *drm_enc)
 {
-	struct dpu_encoder_virt *dpu_enc;
-	struct dpu_encoder_phys *phys;
-	int framecount = 0;
-
-	dpu_enc = to_dpu_encoder_virt(drm_enc);
-	phys = dpu_enc ? dpu_enc->cur_master : NULL;
-
-	if (phys && phys->ops.get_frame_count)
-		framecount = phys->ops.get_frame_count(phys);
-
-	return framecount;
+	struct dpu_encoder_virt *dpu_enc = to_dpu_encoder_virt(drm_enc);
+	struct dpu_encoder_phys *phys = dpu_enc ? dpu_enc->cur_master : NULL;
+	return phys ? atomic_read(&phys->vsync_cnt) : 0;
 }
 
 int dpu_encoder_get_linecount(struct drm_encoder *drm_enc)

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h

@@ -163,9 +163,9 @@ void dpu_encoder_set_idle_timeout(struct drm_encoder *drm_enc,
 int dpu_encoder_get_linecount(struct drm_encoder *drm_enc);
 
 /**
- * dpu_encoder_get_frame_count - get interface frame count for the encoder.
+ * dpu_encoder_get_vsync_count - get vsync count for the encoder.
  * @drm_enc:    Pointer to previously created drm encoder structure
  */
-int dpu_encoder_get_frame_count(struct drm_encoder *drm_enc);
+int dpu_encoder_get_vsync_count(struct drm_encoder *drm_enc);
 
 #endif /* __DPU_ENCODER_H__ */