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    Subject[PATCH 5.16 0493/1017] drm/bridge: dw-hdmi: use safe format when first in bridge chain
    Date
    From: Neil Armstrong <narmstrong@baylibre.com>

    [ Upstream commit 1528038385c0a706aac9ac165eeb24044fef6825 ]

    When the dw-hdmi bridge is in first place of the bridge chain, this
    means there is no way to select an input format of the dw-hdmi HW
    component.

    Since introduction of display-connector, negotiation was broken since
    the dw-hdmi negotiation code only worked when the dw-hdmi bridge was
    in last position of the bridge chain or behind another bridge also
    supporting input & output format negotiation.

    Commit 7cd70656d128 ("drm/bridge: display-connector: implement bus fmts callbacks")
    was introduced to make negotiation work again by making display-connector
    act as a pass-through concerning input & output format negotiation.

    But in the case where the dw-hdmi is single in the bridge chain, for
    example on Renesas SoCs, with the display-connector bridge the dw-hdmi
    is no more single, breaking output format.

    Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
    Bisected-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
    Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
    Fixes: 6c3c719936da ("drm/bridge: synopsys: dw-hdmi: add bus format negociation")
    Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
    [narmstrong: add proper fixes commit]
    Reviewed-by: Robert Foss <robert.foss@linaro.org>
    Link: https://patchwork.freedesktop.org/patch/msgid/20220204143337.89221-1-narmstrong@baylibre.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
    index e1211a5b334b..25d58dcfc87e 100644
    --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
    +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
    @@ -2551,8 +2551,9 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
    if (!output_fmts)
    return NULL;

    - /* If dw-hdmi is the only bridge, avoid negociating with ourselves */
    - if (list_is_singular(&bridge->encoder->bridge_chain)) {
    + /* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
    + if (list_is_singular(&bridge->encoder->bridge_chain) ||
    + list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
    *num_output_fmts = 1;
    output_fmts[0] = MEDIA_BUS_FMT_FIXED;

    --
    2.34.1


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