Re: [PATCH 01/25] drm/i915/fbc: wait for a vblank instead of 50ms when enabling

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 19-01-16 om 14:35 schreef Paulo Zanoni:
> Instead of waiting for 50ms, just wait until the next vblank, since
> it's the minimum requirement. The whole infrastructure of FBC is based
> on vblanks, so waiting for X vblanks instead of X milliseconds sounds
> like the correct way to go. Besides, 50ms may be less than a vblank on
> super slow modes that may or may not exist.
>
> There are some small improvements in PC state residency (due to the
> fact that we're now using 16ms for the common modes instead of 50ms),
> but the biggest advantage is still the correctness of being
> vblank-based instead of time-based.
>
> v2:
>   - Rebase after changing the patch order.
>   - Update the commit message.
> v3:
>   - Fix bogus vblank_get() instead of vblank_count() (Ville).
>   - Don't forget to call drm_crtc_vblank_{get,put} (Chris, Ville)
>   - Adjust the performance details on the commit message.
>
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h  |  2 +-
>  drivers/gpu/drm/i915/intel_fbc.c | 43 ++++++++++++++++++++++++++++------------
>  2 files changed, 31 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index af30148..33217a4 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -925,9 +925,9 @@ struct i915_fbc {
>  
>  	struct intel_fbc_work {
>  		bool scheduled;
> +		u32 scheduled_vblank;
>  		struct work_struct work;
>  		struct drm_framebuffer *fb;
> -		unsigned long enable_jiffies;
>  	} work;
>  
>  	const char *no_fbc_reason;
> diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
> index a1988a4..6b43ec3 100644
> --- a/drivers/gpu/drm/i915/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/intel_fbc.c
> @@ -381,7 +381,15 @@ static void intel_fbc_work_fn(struct work_struct *__work)
>  		container_of(__work, struct drm_i915_private, fbc.work.work);
>  	struct intel_fbc_work *work = &dev_priv->fbc.work;
>  	struct intel_crtc *crtc = dev_priv->fbc.crtc;
> -	int delay_ms = 50;
> +	struct drm_vblank_crtc *vblank = &dev_priv->dev->vblank[crtc->pipe];
> +
> +	mutex_lock(&dev_priv->fbc.lock);
> +	if (drm_crtc_vblank_get(&crtc->base)) {
> +		DRM_ERROR("vblank not available for FBC on pipe %c\n",
> +			  pipe_name(crtc->pipe));
> +		goto out;
> +	}
> +	mutex_unlock(&dev_priv->fbc.lock);
What does the lock protect here?

~Maarten
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