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From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Cc:     linux-renesas-soc@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Alexandru-Cosmin Gheorghe <Alexandru-Cosmin.Gheorghe@arm.com>,
        Gustavo Padovan <gustavo@padovan.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/2] drm/atomic: Initialise planes with opaque alpha values
Date:   Thu, 20 Sep 2018 14:17:05 +0300
Message-ID: <1760492.77853pnPW8@avalon>
Organization: Ideas on Board Oy
In-Reply-To: <20180919155700.10342-2-kieran.bingham+renesas@ideasonboard.com>
References: <20180919155700.10342-1-kieran.bingham+renesas@ideasonboard.com> <20180919155700.10342-2-kieran.bingham+renesas@ideasonboard.com>
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Hi Kieran,

Thank you for the patch.

On Wednesday, 19 September 2018 18:56:58 EEST Kieran Bingham wrote:
> Planes without an alpha property, using __drm_atomic_helper_plane_reset
> will have their plane state alpha initialised as zero, which represents
> a transparent alpha.
> 
> If this value is then used for the plane, it may not be visible by
> default, and thus doesn't represent a good initialisation state.
> 
> Update the default state->alpha value to DRM_BLEND_ALPHA_OPAQUE
> unconditionally when the plane is reset.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

I believe the decision to use plane->alpha_property->values[1] instead of 
hardcoding DRM_BLEND_ALPHA_OPAQUE comes from earlier versions of the alpha 
patch series that supported driver-specific ranges for the alpha value. The 
current implementation uses DRM_BLEND_ALPHA_OPAQUE unconditionally, and no 
driver modifies the maximum value behind the scene, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c
> b/drivers/gpu/drm/drm_atomic_helper.c index 3cf1aa132778..e49b22381048
> 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -3569,9 +3569,7 @@ void __drm_atomic_helper_plane_reset(struct drm_plane
> *plane, state->plane = plane;
>  	state->rotation = DRM_MODE_ROTATE_0;
> 
> -	/* Reset the alpha value to fully opaque if it matters */
> -	if (plane->alpha_property)
> -		state->alpha = plane->alpha_property->values[1];
> +	state->alpha = DRM_BLEND_ALPHA_OPAQUE;
>  	state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> 
>  	plane->state = state;


-- 
Regards,

Laurent Pinchart