linux-kernel - Re: [PATCH] drm/i915/skl: Don't try to update plane watermarks if they haven't changed

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Message-ID: <871t17ipah.fsf@intel.com>
Date:   Mon, 29 Aug 2016 18:10:46 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Lyude <cpaul@...hat.com>, intel-gfx@...ts.freedesktop.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:     Lyude <cpaul@...hat.com>, Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915/skl: Don't try to update plane watermarks if they haven't changed

On Mon, 29 Aug 2016, Lyude <cpaul@...hat.com> wrote:
> i915 sometimes needs to disable planes in the middle of an atomic
> commit, and then reenable them later in the same commit. Because of
> this, we can't make the assumption that the state of the plane actually
> changed. Since the state of the plane hasn't actually changed, neither
> have it's watermarks. And if the watermarks hasn't changed then we
> haven't populated skl_results with anything, which means we'll end up
> zeroing out a plane's watermarks in the middle of the atomic commit
> without restoring them later.

I would appreciate a (brief) description of what the failure mode is in
this case.

BR,
Jani.


>
> Changes since v1:
>  - Fix incorrect use of "it's"
>
> Signed-off-by: Lyude <cpaul@...hat.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Fixes: 62e0fb880123 ("drm/i915/skl: Update plane watermarks atomically
> during plane updates")
>
> Signed-off-by: Lyude <cpaul@...hat.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 7 ++++++-
>  drivers/gpu/drm/i915/intel_sprite.c  | 9 +++++++--
>  2 files changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index e4e6141..13e47a7 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3448,7 +3448,12 @@ static void skylake_disable_primary_plane(struct drm_plane *primary,
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	int pipe = intel_crtc->pipe;
>  
> -	skl_write_plane_wm(intel_crtc, &dev_priv->wm.skl_results, 0);
> +	/*
> +	 * We only populate skl_results on watermark updates, and if the
> +	 * plane's visiblity isn't actually changing neither is its watermarks.
> +	 */
> +	if (!crtc->primary->state->visible)
> +		skl_write_plane_wm(intel_crtc, &dev_priv->wm.skl_results, 0);
>  
>  	I915_WRITE(PLANE_CTL(pipe, 0), 0);
>  	I915_WRITE(PLANE_SURF(pipe, 0), 0);
> diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
> index 0df783a..73a521f 100644
> --- a/drivers/gpu/drm/i915/intel_sprite.c
> +++ b/drivers/gpu/drm/i915/intel_sprite.c
> @@ -292,8 +292,13 @@ skl_disable_plane(struct drm_plane *dplane, struct drm_crtc *crtc)
>  	const int pipe = intel_plane->pipe;
>  	const int plane = intel_plane->plane + 1;
>  
> -	skl_write_plane_wm(to_intel_crtc(crtc), &dev_priv->wm.skl_results,
> -			   plane);
> +	/*
> +	 * We only populate skl_results on watermark updates, and if the
> +	 * plane's visiblity isn't actually changing neither is its watermarks.
> +	 */
> +	if (!dplane->state->visible)
> +		skl_write_plane_wm(to_intel_crtc(crtc),
> +				   &dev_priv->wm.skl_results, plane);
>  
>  	I915_WRITE(PLANE_CTL(pipe, plane), 0);

-- 
Jani Nikula, Intel Open Source Technology Center