drm/msm/dpu: Add mutex lock in control vblank irq

Add a mutex lock to control vblank irq to synchronize vblank
enable/disable operations happening from different threads to prevent
race conditions while registering/unregistering the vblank irq callback.

v4: -Removed vblank_ctl_lock from dpu_encoder_virt, so it is only a
    parameter of dpu_encoder_phys.
    -Switch from atomic refcnt to a simple int counter as mutex has
    now been added
v3: Mistakenly did not change wording in last version. It is done now.
v2: Slightly changed wording of commit message
Signed-off-by: Paloma Arellano <quic_parellan@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/571854/
Link: https://lore.kernel.org/r/20231212231101.9240-2-quic_parellan@quicinc.comSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

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

@@ -2464,7 +2464,6 @@ void dpu_encoder_phys_init(struct dpu_encoder_phys *phys_enc,
 	phys_enc->enc_spinlock = p->enc_spinlock;
 	phys_enc->enable_state = DPU_ENC_DISABLED;
 
-	atomic_set(&phys_enc->vblank_refcount, 0);
 	atomic_set(&phys_enc->pending_kickoff_cnt, 0);
 	atomic_set(&phys_enc->pending_ctlstart_cnt, 0);
 

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

@@ -155,6 +155,7 @@ enum dpu_intr_idx {
  * @hw_cdm:		Hardware interface to the CDM registers
  * @dpu_kms:		Pointer to the dpu_kms top level
  * @cached_mode:	DRM mode cached at mode_set time, acted on in enable
+ * @vblank_ctl_lock:	Vblank ctl mutex lock to protect vblank_refcount
  * @enabled:		Whether the encoder has enabled and running a mode
  * @split_role:		Role to play in a split-panel configuration
  * @intf_mode:		Interface mode
@@ -184,11 +185,12 @@ struct dpu_encoder_phys {
 	struct dpu_hw_cdm *hw_cdm;
 	struct dpu_kms *dpu_kms;
 	struct drm_display_mode cached_mode;
+	struct mutex vblank_ctl_lock;
 	enum dpu_enc_split_role split_role;
 	enum dpu_intf_mode intf_mode;
 	spinlock_t *enc_spinlock;
 	enum dpu_enc_enable_state enable_state;
-	atomic_t vblank_refcount;
+	int vblank_refcount;
 	atomic_t vsync_cnt;
 	atomic_t underrun_cnt;
 	atomic_t pending_ctlstart_cnt;

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

@@ -246,7 +246,8 @@ static int dpu_encoder_phys_cmd_control_vblank_irq(
 		return -EINVAL;
 	}
 
-	refcount = atomic_read(&phys_enc->vblank_refcount);
+	mutex_lock(&phys_enc->vblank_ctl_lock);
+	refcount = phys_enc->vblank_refcount;
 
 	/* Slave encoders don't report vblank */
 	if (!dpu_encoder_phys_cmd_is_master(phys_enc))
@@ -262,16 +263,24 @@ static int dpu_encoder_phys_cmd_control_vblank_irq(
 		      phys_enc->hw_pp->idx - PINGPONG_0,
 		      enable ? "true" : "false", refcount);
 
-	if (enable && atomic_inc_return(&phys_enc->vblank_refcount) == 1)
+	if (enable) {
+		if (phys_enc->vblank_refcount == 0)
 			ret = dpu_core_irq_register_callback(phys_enc->dpu_kms,
 					phys_enc->irq[INTR_IDX_RDPTR],
 					dpu_encoder_phys_cmd_te_rd_ptr_irq,
 					phys_enc);
-	else if (!enable && atomic_dec_return(&phys_enc->vblank_refcount) == 0)
+		if (!ret)
+			phys_enc->vblank_refcount++;
+	} else if (!enable) {
+		if (phys_enc->vblank_refcount == 1)
 			ret = dpu_core_irq_unregister_callback(phys_enc->dpu_kms,
 					phys_enc->irq[INTR_IDX_RDPTR]);
+		if (!ret)
+			phys_enc->vblank_refcount--;
+	}
 
 end:
+	mutex_unlock(&phys_enc->vblank_ctl_lock);
 	if (ret) {
 		DRM_ERROR("vblank irq err id:%u pp:%d ret:%d, enable %s/%d\n",
 			  DRMID(phys_enc->parent),
@@ -287,7 +296,7 @@ static void dpu_encoder_phys_cmd_irq_control(struct dpu_encoder_phys *phys_enc,
 {
 	trace_dpu_enc_phys_cmd_irq_ctrl(DRMID(phys_enc->parent),
 			phys_enc->hw_pp->idx - PINGPONG_0,
-			enable, atomic_read(&phys_enc->vblank_refcount));
+			enable, phys_enc->vblank_refcount);
 
 	if (enable) {
 		dpu_core_irq_register_callback(phys_enc->dpu_kms,
@@ -728,6 +737,9 @@ struct dpu_encoder_phys *dpu_encoder_phys_cmd_init(struct drm_device *dev,
 
 	dpu_encoder_phys_init(phys_enc, p);
 
+	mutex_init(&phys_enc->vblank_ctl_lock);
+	phys_enc->vblank_refcount = 0;
+
 	dpu_encoder_phys_cmd_init_ops(&phys_enc->ops);
 	phys_enc->intf_mode = INTF_MODE_CMD;
 	cmd_enc->stream_sel = 0;

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

@@ -366,7 +366,8 @@ static int dpu_encoder_phys_vid_control_vblank_irq(
 	int ret = 0;
 	int refcount;
 
-	refcount = atomic_read(&phys_enc->vblank_refcount);
+	mutex_lock(&phys_enc->vblank_ctl_lock);
+	refcount = phys_enc->vblank_refcount;
 
 	/* Slave encoders don't report vblank */
 	if (!dpu_encoder_phys_vid_is_master(phys_enc))
@@ -379,18 +380,26 @@ static int dpu_encoder_phys_vid_control_vblank_irq(
 	}
 
 	DRM_DEBUG_VBL("id:%u enable=%d/%d\n", DRMID(phys_enc->parent), enable,
-		      atomic_read(&phys_enc->vblank_refcount));
+		      refcount);
 
-	if (enable && atomic_inc_return(&phys_enc->vblank_refcount) == 1)
+	if (enable) {
+		if (phys_enc->vblank_refcount == 0)
 			ret = dpu_core_irq_register_callback(phys_enc->dpu_kms,
 					phys_enc->irq[INTR_IDX_VSYNC],
 					dpu_encoder_phys_vid_vblank_irq,
 					phys_enc);
-	else if (!enable && atomic_dec_return(&phys_enc->vblank_refcount) == 0)
+		if (!ret)
+			phys_enc->vblank_refcount++;
+	} else if (!enable) {
+		if (phys_enc->vblank_refcount == 1)
 			ret = dpu_core_irq_unregister_callback(phys_enc->dpu_kms,
 					phys_enc->irq[INTR_IDX_VSYNC]);
+		if (!ret)
+			phys_enc->vblank_refcount--;
+	}
 
 end:
+	mutex_unlock(&phys_enc->vblank_ctl_lock);
 	if (ret) {
 		DRM_ERROR("failed: id:%u intf:%d ret:%d enable:%d refcnt:%d\n",
 			  DRMID(phys_enc->parent),
@@ -614,7 +623,7 @@ static void dpu_encoder_phys_vid_irq_control(struct dpu_encoder_phys *phys_enc,
 	trace_dpu_enc_phys_vid_irq_ctrl(DRMID(phys_enc->parent),
 			    phys_enc->hw_intf->idx - INTF_0,
 			    enable,
-			    atomic_read(&phys_enc->vblank_refcount));
+			   phys_enc->vblank_refcount);
 
 	if (enable) {
 		ret = dpu_encoder_phys_vid_control_vblank_irq(phys_enc, true);
@@ -707,6 +716,8 @@ struct dpu_encoder_phys *dpu_encoder_phys_vid_init(struct drm_device *dev,
 	DPU_DEBUG_VIDENC(phys_enc, "\n");
 
 	dpu_encoder_phys_init(phys_enc, p);
+	mutex_init(&phys_enc->vblank_ctl_lock);
+	phys_enc->vblank_refcount = 0;
 
 	dpu_encoder_phys_vid_init_ops(&phys_enc->ops);
 	phys_enc->intf_mode = INTF_MODE_VIDEO;