Re: [PATCH 6/8] drm/msm: dpu: Separate crtc assignment from vblank enable

[Jeykumar Sankaran <jsanka-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 2018-11-13 12:52, Sean Paul wrote:
> From: Sean Paul <seanpaul@chromium.org>
> 
> Instead of assigning/clearing the crtc on vblank enable/disable, we can
> just assign and clear the crtc on modeset. That allows us to just 
> toggle
> the encoder's vblank interrupts on vblank_enable.
> 
> So why is this important? Previously the driver was using the legacy
> pointers to assign/clear the crtc. Legacy pointers are cleared _after_
Which pointers are you referring here as legacy pointers? CRTC?
> disabling the hardware, so the legacy pointer was valid during
> vblank_disable, but that's not something we should rely on.
> 
> Instead of relying on the core ordering the legacy pointer assignments
> just so, we'll assign the crtc in dpu_crtc enable/disable. This is the
> only place that mapping can change, so we're covered there.
> 
> We're also taking advantage of drm_crtc_vblank_on/off. By using this, 
> we
> ensure that vblank_enable/disable can never be called while the crtc is
> off (which means the assigned crtc will always be valid). As such, we

What about the drm_vblank_enable/disable triggered by drm_vblank_get 
when crtc
is disabled? What is the expected behavior there? the vblank_requested
variable removed by the next patch was introduced to cache the request.

> don't need to use modeset locks or the crtc_lock in the
> vblank_enable/disable routine to be sure state is consistent.
> 
> ...I think.
> 
> Signed-off-by: Sean Paul <seanpaul@chromium.org>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c    | 77 +++++++++------------
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 27 +++++---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h | 10 +++
>  3 files changed, 59 insertions(+), 55 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> index 4b7f98a6ab60..59e823281fdf 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
> @@ -757,43 +757,6 @@ void dpu_crtc_commit_kickoff(struct drm_crtc 
> *crtc)
>  	DPU_ATRACE_END("crtc_commit");
>  }
> 
> -/**
> - * _dpu_crtc_vblank_enable_no_lock - update power resource and vblank
> request
> - * @dpu_crtc: Pointer to dpu crtc structure
> - * @enable: Whether to enable/disable vblanks
> - */
> -static void _dpu_crtc_vblank_enable_no_lock(
> -		struct dpu_crtc *dpu_crtc, bool enable)
> -{
> -	struct drm_crtc *crtc = &dpu_crtc->base;
> -	struct drm_device *dev = crtc->dev;
> -	struct drm_encoder *enc;
> -
> -	if (enable) {
> -		list_for_each_entry(enc, &dev->mode_config.encoder_list,
> head) {
> -			if (enc->crtc != crtc)
> -				continue;
> -
> -
> trace_dpu_crtc_vblank_enable(DRMID(&dpu_crtc->base),
> -						     DRMID(enc), enable,
> -						     dpu_crtc);
> -
> -			dpu_encoder_assign_crtc(enc, crtc);
> -		}
> -	} else {
> -		list_for_each_entry(enc, &dev->mode_config.encoder_list,
> head) {
> -			if (enc->crtc != crtc)
> -				continue;
> -
> -
> trace_dpu_crtc_vblank_enable(DRMID(&dpu_crtc->base),
> -						     DRMID(enc), enable,
> -						     dpu_crtc);
> -
> -			dpu_encoder_assign_crtc(enc, NULL);
> -		}
> -	}
> -}
> -
>  /**
>   * dpu_crtc_duplicate_state - state duplicate hook
>   * @crtc: Pointer to drm crtc structure
> @@ -847,6 +810,10 @@ static void dpu_crtc_disable(struct drm_crtc 
> *crtc,
>  	/* Disable/save vblank irq handling */
>  	drm_crtc_vblank_off(crtc);
> 
> +	drm_for_each_encoder_mask(encoder, crtc->dev,
> +				  old_crtc_state->encoder_mask)
> +		dpu_encoder_assign_crtc(encoder, NULL);
> +
>  	mutex_lock(&dpu_crtc->crtc_lock);
> 
>  	/* wait for frame_event_done completion */
> @@ -856,9 +823,6 @@ static void dpu_crtc_disable(struct drm_crtc *crtc,
>  				atomic_read(&dpu_crtc->frame_pending));
> 
>  	trace_dpu_crtc_disable(DRMID(crtc), false, dpu_crtc);
> -	if (dpu_crtc->enabled && dpu_crtc->vblank_requested) {
> -		_dpu_crtc_vblank_enable_no_lock(dpu_crtc, false);
> -	}
>  	dpu_crtc->enabled = false;
> 
>  	if (atomic_read(&dpu_crtc->frame_pending)) {
> @@ -922,13 +886,13 @@ static void dpu_crtc_enable(struct drm_crtc 
> *crtc,
> 
>  	mutex_lock(&dpu_crtc->crtc_lock);
>  	trace_dpu_crtc_enable(DRMID(crtc), true, dpu_crtc);
> -	if (!dpu_crtc->enabled && dpu_crtc->vblank_requested) {
> -		_dpu_crtc_vblank_enable_no_lock(dpu_crtc, true);
> -	}
>  	dpu_crtc->enabled = true;
> 
>  	mutex_unlock(&dpu_crtc->crtc_lock);
> 
> +	drm_for_each_encoder_mask(encoder, crtc->dev,
> crtc->state->encoder_mask)
> +		dpu_encoder_assign_crtc(encoder, crtc);
> +
>  	/* Enable/restore vblank irq handling */
>  	drm_crtc_vblank_on(crtc);
>  }
> @@ -1173,10 +1137,33 @@ static int dpu_crtc_atomic_check(struct 
> drm_crtc
> *crtc,
>  int dpu_crtc_vblank(struct drm_crtc *crtc, bool en)
>  {
>  	struct dpu_crtc *dpu_crtc = to_dpu_crtc(crtc);
> +	struct drm_encoder *enc;
> 
> -	mutex_lock(&dpu_crtc->crtc_lock);
>  	trace_dpu_crtc_vblank(DRMID(&dpu_crtc->base), en, dpu_crtc);
> -	_dpu_crtc_vblank_enable_no_lock(dpu_crtc, en);
> +
> +	/*
> +	 * Normally we would iterate through encoder_mask in crtc state to
> find
> +	 * attached encoders. In this case, we might be disabling vblank
> _after_
> +	 * encoder_mask has been cleared.
> +	 *
> +	 * Instead, we "assign" a crtc to the encoder in enable and clear
> it in
> +	 * disable (which is also after encoder_mask is cleared). So
> instead of
> +	 * using encoder mask, we'll ask the encoder to toggle itself iff
> it's
> +	 * currently assigned to our crtc.
> +	 *
> +	 * Note also that this function cannot be called while crtc is
> disabled
> +	 * since we use drm_crtc_vblank_on/off. So we don't need to worry
> +	 * about the assigned crtcs being inconsistent with the current
> state
> +	 * (which means no need to worry about modeset locks).
> +	 */
> +	list_for_each_entry(enc, &crtc->dev->mode_config.encoder_list,
> head) {
> +		trace_dpu_crtc_vblank_enable(DRMID(crtc), DRMID(enc), en,
> +					     dpu_crtc);
> +
> +		dpu_encoder_toggle_vblank_for_crtc(enc, crtc, en);
> +	}
> +
> +	mutex_lock(&dpu_crtc->crtc_lock);
>  	dpu_crtc->vblank_requested = en;
>  	mutex_unlock(&dpu_crtc->crtc_lock);
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index fd6514f681ae..5914ae70572c 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -1267,22 +1267,29 @@ void dpu_encoder_assign_crtc(struct drm_encoder
> *drm_enc, struct drm_crtc *crtc)
>  {
>  	struct dpu_encoder_virt *dpu_enc = to_dpu_encoder_virt(drm_enc);
>  	unsigned long lock_flags;
> -	bool enable;
> -	int i;
> -
> -	enable = crtc ? true : false;
> -
> -	if (!drm_enc) {
> -		DPU_ERROR("invalid encoder\n");
> -		return;
> -	}
> -	trace_dpu_enc_vblank_cb(DRMID(drm_enc), enable);
> 
>  	spin_lock_irqsave(&dpu_enc->enc_spinlock, lock_flags);
>  	/* crtc should always be cleared before re-assigning */
>  	WARN_ON(crtc && dpu_enc->crtc);
>  	dpu_enc->crtc = crtc;
>  	spin_unlock_irqrestore(&dpu_enc->enc_spinlock, lock_flags);
> +}
> +
> +void dpu_encoder_toggle_vblank_for_crtc(struct drm_encoder *drm_enc,
> +					struct drm_crtc *crtc, bool
> enable)
> +{
> +	struct dpu_encoder_virt *dpu_enc = to_dpu_encoder_virt(drm_enc);
> +	unsigned long lock_flags;
> +	int i;
> +
> +	trace_dpu_enc_vblank_cb(DRMID(drm_enc), enable);
> +
> +	spin_lock_irqsave(&dpu_enc->enc_spinlock, lock_flags);
> +	if (dpu_enc->crtc == crtc) {
> +		spin_unlock_irqrestore(&dpu_enc->enc_spinlock,
> lock_flags);
> +		return;
> +	}
Why are you returning when the crtc's are same?
Won't they be same all the time between modesets?

for both enable/disable crtc will be the same and you still need to call 
the
for loop below to enable/disable the phys encoders.

> +	spin_unlock_irqrestore(&dpu_enc->enc_spinlock, lock_flags);
> 
>  	for (i = 0; i < dpu_enc->num_phys_encs; i++) {
>  		struct dpu_encoder_phys *phys = dpu_enc->phys_encs[i];
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
> b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
> index be1d80867834..6896ea2ab854 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
> @@ -62,6 +62,16 @@ void dpu_encoder_get_hw_resources(struct drm_encoder
> *encoder,
>  void dpu_encoder_assign_crtc(struct drm_encoder *encoder,
>  			     struct drm_crtc *crtc);
> 
> +/**
> + * dpu_encoder_toggle_vblank_for_crtc - Toggles vblank interrupts on 
> or
> off if
> + *	the encoder is assigned to the given crtc
> + * @encoder:	encoder pointer
> + * @crtc:	crtc pointer
> + * @enable:	true if vblank should be enabled
> + */
> +void dpu_encoder_toggle_vblank_for_crtc(struct drm_encoder *encoder,
> +					struct drm_crtc *crtc, bool
> enable);
> +
>  /**
>   * dpu_encoder_register_frame_event_callback - provide callback to
> encoder that
>   *	will be called after the request is complete, or other events.

-- 
Jeykumar S
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