linux-kernel - Re: [PATCH 2/3] arm64: dts: ti: k3-j721e-main.dtsi: Add DSS node

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Date:   Mon, 27 Apr 2020 14:15:25 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Jyri Sarha <jsarha@...com>, Tero Kristo <t-kristo@...com>,
        Nishanth Menon <nm@...com>, Rob Herring <robh+dt@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] arm64: dts: ti: k3-j721e-main.dtsi: Add DSS node

On 27/04/2020 14:10, Jyri Sarha wrote:
> On 27/04/2020 13:51, Tomi Valkeinen wrote:
>> On 27/04/2020 13:37, Jyri Sarha wrote:
>>> On 27/04/2020 13:09, Tero Kristo wrote:
>>>>> +        status = "disabled";
>>>>
>>>> Again, why disabled by default?
>>>>
>>>
>>> tidss device is not functional without a defined video-port. The driver
>>> is not implemented in a way that it would handle a broken configuration
>>> gracefully.
>>
>> Then we need to fix it. The driver should handle the case where there
>> are no ports defined just fine.
>>
> 
> Just by reading the code, I would say that currently the probe would
> fail with returned -ENOMEM after calling drm_vblank_init() with zero CRTCs.
> 
> So should the probe fail gracefully and silently, or should we try to
> register a DRM device with no CRTCs? Is that even possible?

My first thought is that the driver should exit probe silently with ENODEV if there are no outputs 
defined (but, of course, with EPROBE_DEFER if there are outputs which haven't been probed yet).

It gets a bit more complex if we ever support writeback, as that can be used as mem-to-mem without 
any displays, but I think we can ignore that for now.

  Tomi

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