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

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Date:   Mon, 17 Jan 2022 16:53:59 +0000
From:   Marcel Ziswiler <marcel.ziswiler@...adex.com>
To:     "robert.foss@...aro.org" <robert.foss@...aro.org>,
        "narmstrong@...libre.com" <narmstrong@...libre.com>
CC:     "Laurent.pinchart@...asonboard.com" 
        <Laurent.pinchart@...asonboard.com>,
        "kieran.bingham@...asonboard.com" <kieran.bingham@...asonboard.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "biju.das.jz@...renesas.com" <biju.das.jz@...renesas.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jonas@...boo.se" <jonas@...boo.se>,
        "jernej.skrabec@...il.com" <jernej.skrabec@...il.com>,
        "kieran.bingham+renesas@...asonboard.com" 
        <kieran.bingham+renesas@...asonboard.com>
Subject: Re: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge
 chain

Hi Neil

Sorry, just some trivial spelling fixes.

On Mon, 2022-01-17 at 15:17 +0100, Neil Armstrong wrote:
> When the dw-hdmi bridge is in first place of the bridge chain, this
> means there is now way

no way

> to select an input format of the dw-hdmi HW
> component.
> 
> Since introduction of display-connector, negociation

:%s/negociation/negotiation/g

> was broken since
> the dw-hdmi negociation 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 negociation.
> 
> Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks")
> was introduced to make negociation work again by making display-connector
> act as a pass-through concerning input & output format negociation.
> 
> But in the case were

where

> the dw-hdmi was single in the bridge chain, for
> example on Renesas SoCs, with the disply-connector

display-connector

> bridge the dw-hdmi
> is no more single, breaking output format.
> 
> Reported-by: Biju Das <biju.das.jz@...renesas.com>
> Bisected-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> Tested-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts callbacks").
> Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++--
>  1 file changed, 7 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..9f2e1cac0ae2 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;
>  
> @@ -2673,6 +2674,10 @@ static u32 *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>         if (!input_fmts)
>                 return NULL;
>  
> +       /* If dw-hdmi is the first bridge fall-back to safe output format */
> +       if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
> +               output_fmt = MEDIA_BUS_FMT_FIXED;
> +
>         switch (output_fmt) {
>         /* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
>         case MEDIA_BUS_FMT_FIXED:

Cheers

Marcel