linux-kernel - Re: [PATCH 2/2] drm: rcar-du: Enable alpha property on primary planes

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Message-ID: <1604918.OXgyMDt7RE@avalon>
Date:   Thu, 20 Sep 2018 14:22:38 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
Cc:     linux-renesas-soc@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Alexandru-Cosmin Gheorghe <Alexandru-Cosmin.Gheorghe@....com>,
        David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm: rcar-du: Enable alpha property on primary planes

Hi Kieran,

Thank you for the patch.

On Wednesday, 19 September 2018 18:56:59 EEST Kieran Bingham wrote:
> If the alpha property is not added to a plane, a default value will be
> used, which can result in a non-visible layer if the alpha is
> initialised as 0.
> 
> Provide an alpha blend property on all planes.
> 
> Fixes: 161ad653d6c9 ("drm: rcar-du: Use __drm_atomic_helper_plane_reset
> instead of copying the logic")
> 
> Signed-off-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> ---
>  drivers/gpu/drm/rcar-du/rcar_du_plane.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> b/drivers/gpu/drm/rcar-du/rcar_du_plane.c index 9e07758a755c..72399a19d8a6
> 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> @@ -783,13 +783,18 @@ int rcar_du_planes_init(struct rcar_du_group *rgrp)
>  		drm_plane_helper_add(&plane->plane,
>  				     &rcar_du_plane_helper_funcs);
> 
> +		/*
> +		 * The alpha property needs to be initialised on all planes
> +		 * to ensure the correct setting at the output.
> +		 */
> +		drm_plane_create_alpha_property(&plane->plane);
> +

As mentioned in the cover letter, both patches in this series fix the issue at 
hand. The first patch is more generic as it will fix it for all drivers, while 
this patch is specific to the R-Car DU driver. It however makes sense to merge 
it, as it adds alpha support to the primary plane, which can be useful.

Once the first patch gets merged, the above comment won't be correct anymore. 
I wonder whether we shouldn't change the patch description and comment to 
focus on usage of the alpha property for primary planes, and not on the bug 
fix. What's your opinion ?

>  		if (type == DRM_PLANE_TYPE_PRIMARY)
>  			continue;
> 
>  		drm_object_attach_property(&plane->plane.base,
>  					   rcdu->props.colorkey,
>  					   RCAR_DU_COLORKEY_NONE);
> -		drm_plane_create_alpha_property(&plane->plane);
>  		drm_plane_create_zpos_property(&plane->plane, 1, 1, 7);
>  	}

-- 
Regards,

Laurent Pinchart