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

[Robert Foss <robert.foss@linaro.org>]

On Wed, 19 Jan 2022 at 13:28, Neil Armstrong <narmstrong@baylibre.com> 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")

I think this is the wrong hash. Is 7cd70656d128 the actual hash?

> 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").

This hash too.

> 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;
>
> --
> 2.25.1
>

There are two checkstyle issues apart from the above mentioned hash
issues, and I think we can ignore those. With the above mentioned
issue fixed, feel free to add my r-b.

Reviewed-by: Robert Foss <robert.foss@linaro.org>