linux-kernel - Re: dw_hdmi is showing wrong colour after commit 7cd70656d1285b79("drm/bridge: display-connector: implement bus fmts callbacks")

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Date:   Fri, 14 Jan 2022 09:23:51 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Fabio Estevam <festevam@...il.com>,
        Biju Das <biju.das.jz@...renesas.com>
Cc:     "daniel@...ll.ch" <daniel@...ll.ch>,
        "Laurent.pinchart@...asonboard.com" 
        <Laurent.pinchart@...asonboard.com>,
        "robert.foss@...aro.org" <robert.foss@...aro.org>,
        "jonas@...boo.se" <jonas@...boo.se>,
        "jernej.skrabec@...il.com" <jernej.skrabec@...il.com>,
        "martin.blumenstingl@...glemail.com" 
        <martin.blumenstingl@...glemail.com>,
        "linux-amlogic@...ts.infradead.org" 
        <linux-amlogic@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: dw_hdmi is showing wrong colour after commit
 7cd70656d1285b79("drm/bridge: display-connector: implement bus fmts
 callbacks")

Hi,

On 13/01/2022 21:01, Fabio Estevam wrote:
> Hi Biju,
> 
> On Thu, Jan 13, 2022 at 2:45 PM Biju Das <biju.das.jz@...renesas.com> wrote:
>>
>> Hi All,
>>
>> RZ/G2{H, M, N} SoC has dw_hdmi IP and it was working ok(colour) till the commit
>> 7cd70656d1285b79("drm/bridge: display-connector: implement bus fmts callbacks").
>>
>> After this patch, the screen becomes greenish(may be it is setting it into YUV format??).
>>
>> By checking the code, previously it used to call get_input_fmt callback and set colour as RGB24.
>>
>> After this commit, it calls get_output_fmt_callbck and returns 3 outputformats(YUV16, YUV24 and RGB24)
>> And get_input_fmt callback, I see the outputformat as YUV16 instead of RGB24.
>>
>> Not sure, I am the only one seeing this issue with dw_HDMI driver.

This patch was introduced to maintain the bridge color format negotiation after using DRM_BRIDGE_ATTACH_NO_CONNECTOR,
but it seems it behaves incorrectly if the first bridge doesn't implement the negotiation callbacks.

Let me check the code to see how to fix that.

> 
> I have tested linux-next 20220112 on a imx6q-sabresd board, which shows:
> 
> dwhdmi-imx 120000.hdmi: Detected HDMI TX controller v1.30a with HDCP
> (DWC HDMI 3D TX PHY)
> 
> The colors are shown correctly here.
> 

The imx doesn't use DRM_BRIDGE_ATTACH_NO_CONNECTOR so the negotiation fails and use the RGB fallback input & output format.

Anyway thanks for testing

Neil