drm/sun4i: Add support for plane alpha

Our backend supports a per-plane alpha property. Support it through our new
helper.

Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/13e89f0d2f2b55752a22eb8c4f37f325246a3a9c.1523432341.git-series.maxime.ripard@bootlin.com
diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.h b/drivers/gpu/drm/sun4i/sun4i_backend.h
index 316f217..4caee03 100644
--- a/drivers/gpu/drm/sun4i/sun4i_backend.h
+++ b/drivers/gpu/drm/sun4i/sun4i_backend.h
@@ -68,12 +68,15 @@
 #define SUN4I_BACKEND_CKMIN_REG			0x884
 #define SUN4I_BACKEND_CKCFG_REG			0x888
 #define SUN4I_BACKEND_ATTCTL_REG0(l)		(0x890 + (0x4 * (l)))
+#define SUN4I_BACKEND_ATTCTL_REG0_LAY_GLBALPHA_MASK	GENMASK(31, 24)
+#define SUN4I_BACKEND_ATTCTL_REG0_LAY_GLBALPHA(x)		((x) << 24)
 #define SUN4I_BACKEND_ATTCTL_REG0_LAY_PIPESEL_MASK	BIT(15)
 #define SUN4I_BACKEND_ATTCTL_REG0_LAY_PIPESEL(x)		((x) << 15)
 #define SUN4I_BACKEND_ATTCTL_REG0_LAY_PRISEL_MASK	GENMASK(11, 10)
 #define SUN4I_BACKEND_ATTCTL_REG0_LAY_PRISEL(x)			((x) << 10)
 #define SUN4I_BACKEND_ATTCTL_REG0_LAY_YUVEN		BIT(2)
 #define SUN4I_BACKEND_ATTCTL_REG0_LAY_VDOEN		BIT(1)
+#define SUN4I_BACKEND_ATTCTL_REG0_LAY_GLBALPHA_EN	BIT(0)
 
 #define SUN4I_BACKEND_ATTCTL_REG1(l)		(0x8a0 + (0x4 * (l)))
 #define SUN4I_BACKEND_ATTCTL_REG1_LAY_HSCAFCT		GENMASK(15, 14)