Message-ID: <20190821162752.GG104440@art_vandelay>
Date:   Wed, 21 Aug 2019 12:27:52 -0400
From:   Sean Paul <sean@...rly.run>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, Sean Paul <seanpaul@...omium.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jeykumar Sankaran <jsanka@...eaurora.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Jayant Shekhar <jshekhar@...eaurora.org>,
        Bruce Wang <bzwang@...omium.org>,
        Sravanthi Kollukuduru <skolluku@...eaurora.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Fritz Koenig <frkoenig@...gle.com>,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dpu: fix "frame done" timeouts

On Tue, Aug 20, 2019 at 04:12:28PM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> Previously, dpu_crtc_frame_event_work() would try to aquire all the
> modeset locks in order to check whether it can release bandwidth.  (If
> we only have cmd-mode display, bandwidth can be released at frame-done
> time.)
> 
> The problem with this is that it is also responsible for signalling
> frame_done_comp, which dpu_crtc_commit_kickoff() waits on if there is
> already a frame pending.  This is called in the msm_atomic_commit_tail()
> path.. which means that for non-nonblock commits, at least some of the
> modeset locks are already held.
> 
> Re-work this scheme to use a reference count to track our need to have
> clocks enabled.  It is incremented for each atomic commit, and
> decremented in the corresponding frame-done.  Additionally, any crtc
> used in video mode hold an extra reference while they are enabled.  The
> net effect is that we can determine in frame-done whether it is safe to
> drop bandwidth without needing to aquire any modeset locks.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>

All looks good to me, nice cleanup!

Reviewed-by: Sean Paul <sean@...omium.org>

> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c | 16 +------
>  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c      | 45 +++++++++++--------
>  drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c       |  2 +
>  drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h       |  8 ++++
>  4 files changed, 38 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
> index 5cda96875e03..09a49b59bb5b 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_core_perf.c
> @@ -214,7 +214,6 @@ static int _dpu_core_perf_crtc_update_bus(struct dpu_kms *kms,
>   */
>  void dpu_core_perf_crtc_release_bw(struct drm_crtc *crtc)
>  {
> -	struct drm_crtc *tmp_crtc;
>  	struct dpu_crtc *dpu_crtc;
>  	struct dpu_crtc_state *dpu_cstate;
>  	struct dpu_kms *kms;
> @@ -233,22 +232,9 @@ void dpu_core_perf_crtc_release_bw(struct drm_crtc *crtc)
>  	dpu_crtc = to_dpu_crtc(crtc);
>  	dpu_cstate = to_dpu_crtc_state(crtc->state);
>  
> -	/* only do this for command mode rt client */
> -	if (dpu_crtc_get_intf_mode(crtc) != INTF_MODE_CMD)
> +	if (atomic_dec_return(&kms->bandwidth_ref) > 0)
>  		return;
>  
> -	/*
> -	 * If video interface present, cmd panel bandwidth cannot be
> -	 * released.
> -	 */
> -	if (dpu_crtc_get_intf_mode(crtc) == INTF_MODE_CMD)
> -		drm_for_each_crtc(tmp_crtc, crtc->dev) {
> -			if (tmp_crtc->enabled &&
> -				dpu_crtc_get_intf_mode(tmp_crtc) ==
> -						INTF_MODE_VIDEO)
> -				return;
> -		}
> -
>  	/* Release the bandwidth */
>  	if (kms->perf.enable_bw_release) {
>  		trace_dpu_cmd_release_bw(crtc->base.id);
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> index b3417d56032d..4e54550c4a80 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> @@ -292,19 +292,6 @@ void dpu_crtc_vblank_callback(struct drm_crtc *crtc)
>  	trace_dpu_crtc_vblank_cb(DRMID(crtc));
>  }
>  
> -static void dpu_crtc_release_bw_unlocked(struct drm_crtc *crtc)
> -{
> -	int ret = 0;
> -	struct drm_modeset_acquire_ctx ctx;
> -
> -	DRM_MODESET_LOCK_ALL_BEGIN(crtc->dev, ctx, 0, ret);
> -	dpu_core_perf_crtc_release_bw(crtc);
> -	DRM_MODESET_LOCK_ALL_END(ctx, ret);
> -	if (ret)
> -		DRM_ERROR("Failed to acquire modeset locks to release bw, %d\n",
> -			  ret);
> -}
> -
>  static void dpu_crtc_frame_event_work(struct kthread_work *work)
>  {
>  	struct dpu_crtc_frame_event *fevent = container_of(work,
> @@ -334,7 +321,7 @@ static void dpu_crtc_frame_event_work(struct kthread_work *work)
>  			/* release bandwidth and other resources */
>  			trace_dpu_crtc_frame_event_done(DRMID(crtc),
>  							fevent->event);
> -			dpu_crtc_release_bw_unlocked(crtc);
> +			dpu_core_perf_crtc_release_bw(crtc);
>  		} else {
>  			trace_dpu_crtc_frame_event_more_pending(DRMID(crtc),
>  								fevent->event);
> @@ -650,7 +637,7 @@ void dpu_crtc_commit_kickoff(struct drm_crtc *crtc, bool async)
>  		dpu_encoder_prepare_for_kickoff(encoder, async);
>  
>  	if (!async) {
> -		/* wait for frame_event_done completion */
> +		/* wait for previous frame_event_done completion */
>  		DPU_ATRACE_BEGIN("wait_for_frame_done_event");
>  		ret = _dpu_crtc_wait_for_frame_done(crtc);
>  		DPU_ATRACE_END("wait_for_frame_done_event");
> @@ -729,6 +716,7 @@ static void dpu_crtc_disable(struct drm_crtc *crtc,
>  	struct drm_encoder *encoder;
>  	struct msm_drm_private *priv;
>  	unsigned long flags;
> +	bool release_bandwidth = false;
>  
>  	if (!crtc || !crtc->dev || !crtc->dev->dev_private || !crtc->state) {
>  		DPU_ERROR("invalid crtc\n");
> @@ -745,8 +733,15 @@ static void dpu_crtc_disable(struct drm_crtc *crtc,
>  	drm_crtc_vblank_off(crtc);
>  
>  	drm_for_each_encoder_mask(encoder, crtc->dev,
> -				  old_crtc_state->encoder_mask)
> +				  old_crtc_state->encoder_mask) {
> +		/* in video mode, we hold an extra bandwidth reference
> +		 * as we cannot drop bandwidth at frame-done if any
> +		 * crtc is being used in video mode.
> +		 */
> +		if (dpu_encoder_get_intf_mode(encoder) == INTF_MODE_VIDEO)
> +			release_bandwidth = true;
>  		dpu_encoder_assign_crtc(encoder, NULL);
> +	}
>  
>  	/* wait for frame_event_done completion */
>  	if (_dpu_crtc_wait_for_frame_done(crtc))
> @@ -760,7 +755,8 @@ static void dpu_crtc_disable(struct drm_crtc *crtc,
>  	if (atomic_read(&dpu_crtc->frame_pending)) {
>  		trace_dpu_crtc_disable_frame_pending(DRMID(crtc),
>  				     atomic_read(&dpu_crtc->frame_pending));
> -		dpu_core_perf_crtc_release_bw(crtc);
> +		if (release_bandwidth)
> +			dpu_core_perf_crtc_release_bw(crtc);
>  		atomic_set(&dpu_crtc->frame_pending, 0);
>  	}
>  
> @@ -792,6 +788,7 @@ static void dpu_crtc_enable(struct drm_crtc *crtc,
>  	struct dpu_crtc *dpu_crtc;
>  	struct drm_encoder *encoder;
>  	struct msm_drm_private *priv;
> +	bool request_bandwidth;
>  
>  	if (!crtc || !crtc->dev || !crtc->dev->dev_private) {
>  		DPU_ERROR("invalid crtc\n");
> @@ -804,9 +801,19 @@ static void dpu_crtc_enable(struct drm_crtc *crtc,
>  	DRM_DEBUG_KMS("crtc%d\n", crtc->base.id);
>  	dpu_crtc = to_dpu_crtc(crtc);
>  
> -	drm_for_each_encoder_mask(encoder, crtc->dev, crtc->state->encoder_mask)
> +	drm_for_each_encoder_mask(encoder, crtc->dev, crtc->state->encoder_mask) {
> +		/* in video mode, we hold an extra bandwidth reference
> +		 * as we cannot drop bandwidth at frame-done if any
> +		 * crtc is being used in video mode.
> +		 */
> +		if (dpu_encoder_get_intf_mode(encoder) == INTF_MODE_VIDEO)
> +			request_bandwidth = true;
>  		dpu_encoder_register_frame_event_callback(encoder,
>  				dpu_crtc_frame_event_cb, (void *)crtc);
> +	}
> +
> +	if (request_bandwidth)
> +		atomic_inc(&_dpu_crtc_get_kms(crtc)->bandwidth_ref);
>  
>  	trace_dpu_crtc_enable(DRMID(crtc), true, dpu_crtc);
>  	dpu_crtc->enabled = true;
> @@ -981,6 +988,8 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
>  		}
>  	}
>  
> +	atomic_inc(&_dpu_crtc_get_kms(crtc)->bandwidth_ref);
> +
>  	rc = dpu_core_perf_crtc_check(crtc, state);
>  	if (rc) {
>  		DPU_ERROR("crtc%d failed performance check %d\n",
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> index 99d0bd569c38..681955eb286f 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> @@ -800,6 +800,8 @@ static int dpu_kms_hw_init(struct msm_kms *kms)
>  		return rc;
>  	}
>  
> +	atomic_set(&dpu_kms->bandwidth_ref, 0);
> +
>  	dpu_kms->mmio = msm_ioremap(dpu_kms->pdev, "mdp", "mdp");
>  	if (IS_ERR(dpu_kms->mmio)) {
>  		rc = PTR_ERR(dpu_kms->mmio);
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> index 9e40f559c51f..fdef016f5ca3 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> @@ -120,6 +120,14 @@ struct dpu_kms {
>  	struct platform_device *pdev;
>  	bool rpm_enabled;
>  	struct dss_module_power mp;
> +
> +	/* reference count bandwidth requests, so we know when we can
> +	 * release bandwidth.  Each atomic update increments, and frame-
> +	 * done event decrements.  Additionally, for video mode, the
> +	 * reference is incremented when crtc is enabled, and decremented
> +	 * when disabled.
> +	 */
> +	atomic_t bandwidth_ref;
>  };
>  
>  struct vsync_info {
> -- 
> 2.21.0
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS

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