Re: [PATCH v5 2/2] drm/i915/display: Prevent DC6 while vblank is enabled for Panel Replay

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Sep 20, 2024 at 09:23:40AM +0300, Jouni Högander wrote:
> We need to block DC6 entry in case of Panel Replay as enabling VBI doesn't
> prevent DC6 in case of Panel Replay. This causes problems if user-space is
> polling for vblank events.
> 
> Fix this by setting target DC state as DC_STATE_EN_UPTO_DC5 when both
> source and sink are supporting eDP Panel Replay and VBI is enabled.
> 
> v4:
>   - s/vblank_work/vblank_dc_work/
>   - changed type of block_dc_for_vblank to bool
> v3:
>   - do flush_work for vblank_work on intel_crtc_vblank_off
>   - no need to use READ_ONCE in bdw_enable_vblank
>   - check crtc->block_dc_for_vblank in bdw_disable_vblank as well
>   - move adding block_dc_for_vblank into this patch
> v2:
>   - use READ_ONCE in intel_display_vblank_work
>   - use DC_STATE_DISABLE instead of DC_STATE_EN_UPTO_DC6
>   - use intel_crtc->block_dc6_needed
> 
> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2296
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_crtc.c     |  7 +++++
>  .../gpu/drm/i915/display/intel_display_core.h |  2 ++
>  .../gpu/drm/i915/display/intel_display_irq.c  | 28 +++++++++++++++++++
>  .../drm/i915/display/intel_display_types.h    |  2 ++
>  4 files changed, 39 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
> index f95d169fc324a..3a28d8450a384 100644
> --- a/drivers/gpu/drm/i915/display/intel_crtc.c
> +++ b/drivers/gpu/drm/i915/display/intel_crtc.c
> @@ -124,6 +124,8 @@ void intel_crtc_vblank_on(const struct intel_crtc_state *crtc_state)
>  {
>  	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
>  
> +	crtc->block_dc_for_vblank = intel_psr_needs_block_dc_vblank(crtc_state);
> +
>  	assert_vblank_disabled(&crtc->base);
>  	drm_crtc_set_max_vblank_count(&crtc->base,
>  				      intel_crtc_max_vblank_count(crtc_state));
> @@ -140,6 +142,7 @@ void intel_crtc_vblank_on(const struct intel_crtc_state *crtc_state)
>  void intel_crtc_vblank_off(const struct intel_crtc_state *crtc_state)
>  {
>  	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> +	struct intel_display *display = to_intel_display(crtc);
>  
>  	/*
>  	 * Should really happen exactly when we disable the pipe
> @@ -150,6 +153,10 @@ void intel_crtc_vblank_off(const struct intel_crtc_state *crtc_state)
>  
>  	drm_crtc_vblank_off(&crtc->base);
>  	assert_vblank_disabled(&crtc->base);
> +
> +	crtc->block_dc_for_vblank = false;
> +
> +	flush_work(&display->irq.vblank_dc_work);
>  }
>  
>  struct intel_crtc_state *intel_crtc_state_alloc(struct intel_crtc *crtc)
> diff --git a/drivers/gpu/drm/i915/display/intel_display_core.h b/drivers/gpu/drm/i915/display/intel_display_core.h
> index 0a711114ff2b4..ac4c005fe3489 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_core.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_core.h
> @@ -457,6 +457,8 @@ struct intel_display {
>  		/* For i915gm/i945gm vblank irq workaround */
>  		u8 vblank_enabled;
>  
> +		struct work_struct vblank_dc_work;
> +
>  		u32 de_irq_mask[I915_MAX_PIPES];
>  		u32 pipestat_irq_mask[I915_MAX_PIPES];
>  	} irq;
> diff --git a/drivers/gpu/drm/i915/display/intel_display_irq.c b/drivers/gpu/drm/i915/display/intel_display_irq.c
> index 0ccbf7a1f2bf6..6878dde85031c 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_irq.c
> +++ b/drivers/gpu/drm/i915/display/intel_display_irq.c
> @@ -1360,9 +1360,27 @@ static bool gen11_dsi_configure_te(struct intel_crtc *intel_crtc,
>  	return true;
>  }
>  
> +static void intel_display_vblank_dc_work(struct work_struct *work)
> +{
> +	struct intel_display *display =
> +		container_of(work, typeof(*display), irq.vblank_dc_work);
> +	struct drm_i915_private *i915 = to_i915(display->drm);
> +	u8 vblank_enabled = READ_ONCE(display->irq.vblank_enabled);
> +
> +	/*
> +	 * NOTE: intel_display_power_set_target_dc_state is used only by PSR
> +	 * code for DC3CO handling. DC3CO target state is currently disabled in
> +	 * PSR code. If DC3CO is taken into use we need take that into account
> +	 * here as well.
> +	 */
> +	intel_display_power_set_target_dc_state(i915, vblank_enabled ? DC_STATE_DISABLE :
> +						DC_STATE_EN_UPTO_DC6);
> +}
> +
>  int bdw_enable_vblank(struct drm_crtc *_crtc)
>  {
>  	struct intel_crtc *crtc = to_intel_crtc(_crtc);
> +	struct intel_display *display = to_intel_display(crtc);
>  	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
>  	enum pipe pipe = crtc->pipe;
>  	unsigned long irqflags;
> @@ -1370,6 +1388,9 @@ int bdw_enable_vblank(struct drm_crtc *_crtc)
>  	if (gen11_dsi_configure_te(crtc, true))
>  		return 0;
>  
> +	if (display->irq.vblank_enabled++ == 0 && crtc->block_dc_for_vblank)
> +		schedule_work(&display->irq.vblank_dc_work);

It occurred to me that this is a little bit broken. If the
first crtc to increment the count does not need the w/a
then we'll not enable the w/a, and it will not get enabled
for other crtcs either until the count has dropped back down
to 0.

I think simply checking crtc->block_dc_for_vblank before
the increment/decrement should fix it.

Yes, that does mean vblank_enabled isn't actually counting
how many crtc have their vblank enabled, but rather how
many crtcs are applying the w/a. To avoid too much
confusion we could simply rename it to something like
vblank_wa_pipes/etc.

> +
>  	spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
>  	bdw_enable_pipe_irq(dev_priv, pipe, GEN8_PIPE_VBLANK);
>  	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
> @@ -1435,6 +1456,7 @@ void ilk_disable_vblank(struct drm_crtc *crtc)
>  void bdw_disable_vblank(struct drm_crtc *_crtc)
>  {
>  	struct intel_crtc *crtc = to_intel_crtc(_crtc);
> +	struct intel_display *display = to_intel_display(crtc);
>  	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
>  	enum pipe pipe = crtc->pipe;
>  	unsigned long irqflags;
> @@ -1445,6 +1467,9 @@ void bdw_disable_vblank(struct drm_crtc *_crtc)
>  	spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
>  	bdw_disable_pipe_irq(dev_priv, pipe, GEN8_PIPE_VBLANK);
>  	spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
> +
> +	if (--display->irq.vblank_enabled == 0 && crtc->block_dc_for_vblank)
> +		schedule_work(&display->irq.vblank_dc_work);
>  }
>  
>  void vlv_display_irq_reset(struct drm_i915_private *dev_priv)
> @@ -1881,4 +1906,7 @@ void intel_display_irq_init(struct drm_i915_private *i915)
>  		i915->display.irq.display_irqs_enabled = false;
>  
>  	intel_hotplug_irq_init(i915);
> +
> +	INIT_WORK(&i915->display.irq.vblank_dc_work,
> +		  intel_display_vblank_dc_work);
>  }
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 3e694c1204dbf..513e843e19b9e 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1413,6 +1413,8 @@ struct intel_crtc {
>  #ifdef CONFIG_DEBUG_FS
>  	struct intel_pipe_crc pipe_crc;
>  #endif
> +
> +	bool block_dc_for_vblank;
>  };
>  
>  struct intel_plane {
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel