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Subject: Re: [PATCH] drm/stm: ltdc: add layer alpha support
To:     Raphael GALLAIS-POU - foss <raphael.gallais-pou@foss.st.com>,
        "Philippe CORNU - foss" <philippe.cornu@foss.st.com>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>
CC:     David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        "Maxime Coquelin" <mcoquelin.stm32@gmail.com>,
        Alexandre TORGUE - foss <alexandre.torgue@foss.st.com>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-stm32@st-md-mailman.stormreply.com" 
        <linux-stm32@st-md-mailman.stormreply.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Raphael GALLAIS-POU <raphael.gallais-pou@st.com>
References: <20210903085740.23108-1-raphael.gallais-pou@foss.st.com>
From:   yannick Fertre <yannick.fertre@foss.st.com>
Message-ID: <19331273-3464-869e-8e62-a0c3e096ed70@foss.st.com>
Date:   Tue, 7 Sep 2021 08:55:14 +0200
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Hi Raphael,
thanks for the patch.

Acked-by: Yannick Fertre <yannick.fertre@foss.st.com>
Reviewed-by: Yannick Fertre <yannick.fertre@foss.st.com>

On 9/3/21 10:58 AM, Raphael GALLAIS-POU - foss wrote:
> Android Hardware Composer supports alpha values applied to layers.
> Enabling non-opaque layers for the STM CRTC could help offload GPU
> resources for screen composition.
> 
> Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
> ---
>   drivers/gpu/drm/stm/ltdc.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 195de30eb90c..e0fef8bacfa8 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -845,7 +845,7 @@ static void ltdc_plane_atomic_update(struct drm_plane *plane,
>   			LXCFBLR_CFBLL | LXCFBLR_CFBP, val);
>   
>   	/* Specifies the constant alpha value */
> -	val = CONSTA_MAX;
> +	val = newstate->alpha >> 8;
>   	reg_update_bits(ldev->regs, LTDC_L1CACR + lofs, LXCACR_CONSTA, val);
>   
>   	/* Specifies the blending factors */
> @@ -997,6 +997,8 @@ static struct drm_plane *ltdc_plane_create(struct drm_device *ddev,
>   
>   	drm_plane_helper_add(plane, &ltdc_plane_helper_funcs);
>   
> +	drm_plane_create_alpha_property(plane);
> +
>   	DRM_DEBUG_DRIVER("plane:%d created\n", plane->base.id);
>   
>   	return plane;
>