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    SubjectRe: [PATCH v2] drm/bridge: dw-hdmi: use safe format when first in bridge chain
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    Hi,

    On 19/01/2022 13:28, Neil Armstrong wrote:
    > 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 0656d1285b79 ("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: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks").
    > Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
    > ---
    > Changes since v1:
    > - Remove bad fix in dw_hdmi_bridge_atomic_get_input_bus_fmts
    > - Fix typos in commit message
    >
    > 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 54d8fdad395f..97cdc61b57f6 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;
    >

    Can a bridge reviewer get an eye on this ? this actually solves an issue reported on a Renesas platform.

    Neil

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