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    Subject[PATCH 4.9 011/137] drm/vc4: ->x_scaling[1] should never be set to VC4_SCALING_NONE
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ 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 70051bf0ee5c..0376c0c2fc66 100644
    --- a/drivers/gpu/drm/vc4/vc4_plane.c
    +++ b/drivers/gpu/drm/vc4/vc4_plane.c
    @@ -345,12 +345,14 @@ 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


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