Nouveau - Aug 2020 - [PATCH AUTOSEL 5.8 17/64] drm/nouveau/kms/nv50-: Fix disabling dithering

From: Lyude Paul <lyude at redhat.com>

[ Upstream commit fb2420b701edbf96c2b6d557f0139902f455dc2b ]

While we expose the ability to turn off hardware dithering for nouveau,
we actually make the mistake of turning it on anyway, due to
dithering_depth containing a non-zero value if our dithering depth isn't
also set to 6 bpc.

So, fix it by never enabling dithering when it's disabled.

Signed-off-by: Lyude Paul <lyude at redhat.com>
Reviewed-by: Ben Skeggs <bskeggs at redhat.com>
Acked-by: Dave Airlie <airlied at gmail.com>
Link:
https://patchwork.freedesktop.org/patch/msgid/20200627194657.156514-6-lyude at
redhat.com
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/gpu/drm/nouveau/dispnv50/head.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/dispnv50/head.c
b/drivers/gpu/drm/nouveau/dispnv50/head.c
index 8f6455697ba72..ed6819519f6d8 100644
--- a/drivers/gpu/drm/nouveau/dispnv50/head.c
+++ b/drivers/gpu/drm/nouveau/dispnv50/head.c
@@ -84,18 +84,20 @@ nv50_head_atomic_check_dither(struct nv50_head_atom *armh,
 {
 	u32 mode = 0x00;
 
-	if (asyc->dither.mode == DITHERING_MODE_AUTO) {
-		if (asyh->base.depth > asyh->or.bpc * 3)
-			mode = DITHERING_MODE_DYNAMIC2X2;
-	} else {
-		mode = asyc->dither.mode;
-	}
+	if (asyc->dither.mode) {
+		if (asyc->dither.mode == DITHERING_MODE_AUTO) {
+			if (asyh->base.depth > asyh->or.bpc * 3)
+				mode = DITHERING_MODE_DYNAMIC2X2;
+		} else {
+			mode = asyc->dither.mode;
+		}
 
-	if (asyc->dither.depth == DITHERING_DEPTH_AUTO) {
-		if (asyh->or.bpc >= 8)
-			mode |= DITHERING_DEPTH_8BPC;
-	} else {
-		mode |= asyc->dither.depth;
+		if (asyc->dither.depth == DITHERING_DEPTH_AUTO) {
+			if (asyh->or.bpc >= 8)
+				mode |= DITHERING_DEPTH_8BPC;
+		} else {
+			mode |= asyc->dither.depth;
+		}
 	}
 
 	asyh->dither.enable = mode;
-- 
2.25.1