Re: [RFR 2/2] drm/panel: Add simple panel support

Tomi Valkeinen
2013-10-17T08:49:52Z

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Hi,

On 17/10/13 11:28, Dave Airlie wrote:
>>
>> My biggest concern here is that this will not be compatible with the CDF DT
>> bindings. They're not complete yet, but they will require connections between
>> entities to be described in DT, in a way very similar (or actually identical)
>> to the V4L2 DT bindings, documented in
>> Documentation/devicetree/bindings/media/video-interfaces.txt. Could you have a
>> look at that ? Please ignore all optional properties beside remote-endpoint,
>> as they're V4L2 specific.
>>
>> I also plan to specify video bus parameters in DT for CDF, but this hasn't
>> been finalized yet.
>>
>
> While I understand this, I don't see why CDF can't enhance these
> bindings if it has
> requirements > than they have without disturbing the panel ones,
>
> is DT really that inflexible?
>
> It seems that have a simple description for basic panels like Thierry wants
> to support, that can be enhanced for the other cases in the future should
> suffice, I really don't like blocking stuff that makes things work on the chance
> of something that isn't upstream yet, its sets a bad precedent, its also breaks
> the perfect is the enemy of good rule

Just my opinion, but yes, DT is that inflexible. DT bindings are like a
syscall. Once they are there, you need to support them forever. That
support can, of course, include some kind of DT data converters or such,
that try to convert old bindings to new bindings at kernel boot.

In practice even such converter may be enough, if some important piece
of data in the new bindings is missing, and this data was implicit in a
driver. In that case the conversion, or parts of it, must be done later,
in that specific driver.

Even that may be difficult, if the piece of data should actually be
handled by some other driver. In that case there's probably need for
some kind of global look-up table or such, so that the drivers can work
around the problem of missing information.

I've been working with DT bindings for OMAP display subsystem for
something like 1.5 years. Still not merged, as they are not perfect, and
I'm scared to push them in non-perfect form, as that could result in
some kind of DT-binding-converter-hell described above.

Tomi

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