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From:   Raphael GALLAIS-POU - foss <raphael.gallais-pou@foss.st.com>
To:     Yannick FERTRE - foss <yannick.fertre@foss.st.com>,
        Philippe CORNU - foss <philippe.cornu@foss.st.com>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>
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        Alexandre TORGUE - foss <alexandre.torgue@foss.st.com>,
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        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Raphael GALLAIS-POU - foss <raphael.gallais-pou@foss.st.com>,
        Raphael GALLAIS-POU <raphael.gallais-pou@st.com>
Subject: [PATCH] drm/stm: ltdc: add layer alpha support
Thread-Topic: [PATCH] drm/stm: ltdc: add layer alpha support
Thread-Index: AQHXoKHtnlZSU/d2YES0y3Gmjn+IKg==
Date:   Fri, 3 Sep 2021 08:58:56 +0000
Message-ID: <20210903085740.23108-1-raphael.gallais-pou@foss.st.com>
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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);
=20
 	/* Specifies the constant alpha value */
-	val =3D CONSTA_MAX;
+	val =3D newstate->alpha >> 8;
 	reg_update_bits(ldev->regs, LTDC_L1CACR + lofs, LXCACR_CONSTA, val);
=20
 	/* Specifies the blending factors */
@@ -997,6 +997,8 @@ static struct drm_plane *ltdc_plane_create(struct drm_d=
evice *ddev,
=20
 	drm_plane_helper_add(plane, &ltdc_plane_helper_funcs);
=20
+	drm_plane_create_alpha_property(plane);
+
 	DRM_DEBUG_DRIVER("plane:%d created\n", plane->base.id);
=20
 	return plane;
--=20
2.17.1