linux-kernel - [PATCH] drm/stm: ltdc: add layer alpha support

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Date:   Tue, 7 Sep 2021 17:12:09 +0200
From:   Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>
To:     Yannick Fertre <yannick.fertre@...s.st.com>,
        Philippe Cornu <philippe.cornu@...s.st.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>
CC:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        "Maxime Coquelin" <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        Raphael Gallais-Pou <raphael.gallais-pou@...com>
Subject: [PATCH] drm/stm: ltdc: add layer alpha support

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@...s.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;
-- 
2.17.1