linux-kernel - Re: [PATCH v16 4/4] drm/bridge: dw-hdmi: fix bus formats negotiation for 8 bit modes

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Date:   Thu, 3 Mar 2022 16:37:06 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Neil Armstrong <narmstrong@...libre.com>
Cc:     Paul Boddie <paul@...die.org.uk>, Jonas Karlman <jonas@...boo.se>,
        David Airlie <airlied@...ux.ie>,
        Robert Foss <robert.foss@...aro.org>,
        linux-mips <linux-mips@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Paul Cercueil <paul@...pouillou.net>,
        Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH v16 4/4] drm/bridge: dw-hdmi: fix bus formats negotiation
 for 8 bit modes

Hi Neil,

> Am 03.03.2022 um 12:45 schrieb H. Nikolaus Schaller <hns@...delico.com>:
> 
> Hi Neil,
> 
>> Am 03.03.2022 um 12:42 schrieb Neil Armstrong <narmstrong@...libre.com>:
>> 
>>> So how can we get that merged? IMHO your proposal should be before we add ingenic-dw-hdmi.
>>> If you have a version with proper commit message I can add it to the beginning of my
>>> seried and include it in a v17. Or if you get yours merged to drm-misc/drm-misc-next I
>>> can build on top.
>> 
>> You can add it in your v17 patchset with my authorship and my Signed-off-by tag + yours.
>> 
>> As commit message something like :
>> ====================
>> drm/bridge: dw-hdmi: handle unusable or non-configured CSC module
>> 
>> The dw-hdmi integrates an optional Color Space Conversion feature used
>> to handle color-space conversions.
>> 
>> On some platforms, the CSC isn't built-in or non-functional.
>> 
>> This adds the necessary code to disable the CSC functionality
>> and limit the bus format negotiation to force using the same
>> input bus format as the output bus format.
>> ====================
> 
> Fine! Will do.

I was a little too early.

While preparing the patches I found that I still had the hack to force
sink_is_hdmi = false in my test branch. Sorry for that.

Removing this made the panel go black again, even with your latest
proposal.

So I looked deeper into your patch and it seems to influence the
input formats only in dw_hdmi_bridge_atomic_get_input_bus_fmts()?

While the problem I see is with output formats and we had worked on
modifying dw_hdmi_bridge_atomic_get_output_bus_fmts().

BR and thanks,
Nikolaus