[Intel-gfx] [PATCH v2 10/16] drm/i915: Wait for watermark updates to finish before disabling a pipe

[Paulo Zanoni]

2014-05-22 11:48 GMT-03:00  <ville.syrjala at linux.intel.com>:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
>
> After we've disabled the planes, it seems like a good idea wait for
> the vblank driven watermark updates to finish before we turn off the
> vblank interrupts and eventually the entire pipe.

Can you please elaborate more on why it is a "good idea"? Is is a real
requirement? A bugfix? What happens if we don't do this?
The answer should be on the commit message.

The only potential problem I could find is that we'll wake up the
waitqueue after ilk_refresh_pending_watermarks() but still before
ilk_program_watermarks(). This doesn't seem to be a problem with the
current code, but is the kid of thing that could lead to future bugs
due to the constant code rewrite/refactor we do. Maybe a comment on
top of the ilk_wm_synchronize() definition - explaining that the
function may return while the register values are still not
"synchronized" - would help a little bit. Or maybe we could just call
wake_up_all() after the registers are written.

With at least the commit message amended: Reviewed-by: Paulo Zanoni
<paulo.r.zanoni at intel.com>

>
> v2: Rebase and s/intel_crtc/crtc/
>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h      |  1 +
>  drivers/gpu/drm/i915/intel_display.c |  2 ++
>  drivers/gpu/drm/i915/intel_drv.h     |  1 +
>  drivers/gpu/drm/i915/intel_pm.c      | 32 ++++++++++++++++++++++++++++++++
>  4 files changed, 36 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 5b1404e..1fe0cac 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1554,6 +1554,7 @@ struct drm_i915_private {
>                 struct mutex mutex;
>
>                 struct work_struct work;
> +               wait_queue_head_t wait;
>         } wm;
>
>         struct i915_runtime_pm pm;
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 5bf1633..ca362db 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3960,6 +3960,8 @@ static void intel_crtc_disable_planes(struct drm_crtc *crtc)
>         intel_disable_planes(crtc);
>         intel_disable_primary_hw_plane(dev_priv, plane, pipe);
>
> +       ilk_wm_synchronize(intel_crtc);
> +
>         drm_vblank_off(dev, pipe);
>  }
>
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 1ec4379..5ad7ad5 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -1021,6 +1021,7 @@ void intel_program_watermarks_pre(struct intel_crtc *crtc,
>                                   const struct intel_crtc_wm_config *config);
>  void intel_program_watermarks_post(struct intel_crtc *crtc,
>                                    const struct intel_crtc_wm_config *config);
> +void ilk_wm_synchronize(struct intel_crtc *crtc);
>
>
>  /* intel_sdvo.c */
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 13366b7..1c072cd 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -2812,6 +2812,7 @@ static bool ilk_pending_watermarks_ready(struct intel_crtc *crtc)
>
>  static bool ilk_refresh_pending_watermarks(struct drm_device *dev)
>  {
> +       struct drm_i915_private *dev_priv = dev->dev_private;
>         struct intel_crtc *crtc;
>         bool changed = false;
>
> @@ -2833,6 +2834,9 @@ static bool ilk_refresh_pending_watermarks(struct drm_device *dev)
>                 changed = true;
>         }
>
> +       if (changed)
> +               wake_up_all(&dev_priv->wm.wait);
> +
>         return changed;
>  }
>
> @@ -3029,6 +3033,33 @@ static void ilk_wm_cancel(struct intel_crtc *crtc)
>         }
>  }
>
> +void ilk_wm_synchronize(struct intel_crtc *crtc)
> +{
> +       struct drm_device *dev = crtc->base.dev;
> +       struct drm_i915_private *dev_priv = dev->dev_private;
> +       enum pipe pipe = crtc->pipe;
> +       unsigned long timeout = msecs_to_jiffies(100);
> +
> +       wait_event_timeout(dev_priv->wm.wait, !crtc->wm.dirty, timeout);
> +
> +       mutex_lock(&dev_priv->wm.mutex);
> +
> +       spin_lock_irq(&crtc->wm.lock);
> +
> +       WARN(crtc->wm.dirty, "pipe %c watermark updates failed to complete\n",
> +            pipe_name(pipe));
> +
> +       /* clean up if something is left behind */
> +       ilk_wm_cancel(crtc);
> +
> +       spin_unlock_irq(&crtc->wm.lock);
> +
> +       /* pending update (if any) got cancelled */
> +       crtc->wm.pending = crtc->wm.active;
> +
> +       mutex_unlock(&dev_priv->wm.mutex);
> +}
> +
>  static int ilk_update_primary_wm(struct intel_crtc *crtc,
>                                  struct intel_crtc_wm_config *config)
>  {
> @@ -6736,6 +6767,7 @@ void intel_init_pm(struct drm_device *dev)
>         struct drm_i915_private *dev_priv = dev->dev_private;
>
>         mutex_init(&dev_priv->wm.mutex);
> +       init_waitqueue_head(&dev_priv->wm.wait);
>         INIT_WORK(&dev_priv->wm.work, ilk_watermark_work);
>
>         if (HAS_FBC(dev)) {
> --
> 1.8.5.5
>
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-- 
Paulo Zanoni