[PATCH AUTOSEL 4.20 033/304] drm/vc4: ->x_scaling[1] should never be set to VC4_SCALING_NONE

[Sasha Levin <sashal@kernel.org>]

From: Boris Brezillon <boris.brezillon@bootlin.com>

[ Upstream commit 0560054da5673b25d56bea6c57c8d069673af73b ]

For the YUV conversion to work properly, ->x_scaling[1] should never
be set to VC4_SCALING_NONE, but vc4_get_scaling_mode() might return
VC4_SCALING_NONE if the horizontal scaling ratio exactly matches the
horizontal subsampling factor. Add a test to turn VC4_SCALING_NONE
into VC4_SCALING_PPF when that happens.

The old ->x_scaling[0] adjustment is dropped as I couldn't find any
mention to this constraint in the spec and it's proven to be
unnecessary (I tested various multi-planar YUV formats with scaling
disabled, and all of them worked fine without this adjustment).

Fixes: fc04023fafec ("drm/vc4: Add support for YUV planes.")
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20181109102633.32603-1-boris.brezillon@bootlin.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/vc4/vc4_plane.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
index ae6254b0b1ae..ed8b0fc170ee 100644
--- a/drivers/gpu/drm/vc4/vc4_plane.c
+++ b/drivers/gpu/drm/vc4/vc4_plane.c
@@ -314,12 +314,14 @@ static int vc4_plane_setup_clipping_and_scaling(struct drm_plane_state *state)
 			vc4_get_scaling_mode(vc4_state->src_h[1],
 					     vc4_state->crtc_h);
 
-		/* YUV conversion requires that horizontal scaling be enabled,
-		 * even on a plane that's otherwise 1:1. Looks like only PPF
-		 * works in that case, so let's pick that one.
+		/* YUV conversion requires that horizontal scaling be enabled
+		 * on the UV plane even if vc4_get_scaling_mode() returned
+		 * VC4_SCALING_NONE (which can happen when the down-scaling
+		 * ratio is 0.5). Let's force it to VC4_SCALING_PPF in this
+		 * case.
 		 */
-		if (vc4_state->is_unity)
-			vc4_state->x_scaling[0] = VC4_SCALING_PPF;
+		if (vc4_state->x_scaling[1] == VC4_SCALING_NONE)
+			vc4_state->x_scaling[1] = VC4_SCALING_PPF;
 	} else {
 		vc4_state->is_yuv = false;
 		vc4_state->x_scaling[1] = VC4_SCALING_NONE;
-- 
2.19.1