Re: [PATCH] drm/i915: Reject changes of fb base when we have a flip pending

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Tue,  4 Mar 2014 13:15:08 +0000
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> This should be impossible due to the wait for outstanding flips that the
> caller is meant to perform prior to updating the scanout base. Paranoia
> tells me to check anyway.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=75502
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 43 ++++++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 25c486d5fb6a..6dc93bd6594f 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -2349,6 +2349,25 @@ intel_finish_fb(struct drm_framebuffer *old_fb)
>  	return ret;
>  }
>  
> +static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
> +{
> +	struct drm_device *dev = crtc->dev;
> +	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> +	unsigned long flags;
> +	bool pending;
> +
> +	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> +	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> +		return false;
> +
> +	spin_lock_irqsave(&dev->event_lock, flags);
> +	pending = to_intel_crtc(crtc)->unpin_work != NULL;
> +	spin_unlock_irqrestore(&dev->event_lock, flags);
> +
> +	return pending;
> +}
> +
>  static int
>  intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
>  		    struct drm_framebuffer *fb)
> @@ -2359,6 +2378,11 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
>  	struct drm_framebuffer *old_fb;
>  	int ret;
>  
> +	if (intel_crtc_has_pending_flip(crtc)) {
> +		DRM_ERROR("pipe is still busy with an old pageflip\n");
> +		return -EBUSY;
> +	}
> +
>  	/* no fb bound */
>  	if (!fb) {
>  		DRM_ERROR("No FB bound\n");
> @@ -2984,25 +3008,6 @@ static void ironlake_fdi_disable(struct drm_crtc *crtc)
>  	udelay(100);
>  }
>  
> -static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
> -{
> -	struct drm_device *dev = crtc->dev;
> -	struct drm_i915_private *dev_priv = dev->dev_private;
> -	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> -	unsigned long flags;
> -	bool pending;
> -
> -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> -	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> -		return false;
> -
> -	spin_lock_irqsave(&dev->event_lock, flags);
> -	pending = to_intel_crtc(crtc)->unpin_work != NULL;
> -	spin_unlock_irqrestore(&dev->event_lock, flags);
> -
> -	return pending;
> -}
> -
>  bool intel_has_pending_fb_unpin(struct drm_device *dev)
>  {
>  	struct intel_crtc *crtc;

Looks fine, my only comment is do we want this to be a DRM_ERROR?  It
would be easy for userspace to trigger this by queueing a flip on a
busy ring, then doing a mode set that ends up doing just a pipe base
update, right?

Otherwise,
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

-- 
Jesse Barnes, Intel Open Source Technology Center