[PATCH v2 0/6] drm/omap: Module parameter for display order configuration

[Tomi Valkeinen]

Hi,

On 28/05/18 13:55, Pekka Paalanen wrote:

>> The series adds support for changing the order of the displays defined by DT
>> display aliases.
>>
>> The motivation to do such a thing is that for example the fb emulation is
>> treating the first display/crtc as the 'main' display and will create the
>> fb emulation based on the first display's properties.
> 
> Hi,
> 
> catering for fbdev seems strange to me. But if you do care, why is this

Strange how? Because we should get rid of it? Sure. But it's there, and
it's being used by almost everyone, at least in the form of fb console.

> a driver-specific option instead of a generic DRM fb emulation
> configuration option?

That'd be fine for me, but I think the actual code to do this
"create-connectors-in-this-order" work is still driver specific. Perhaps
we could have a simple option to just choose the "main" display for
fbdev (without chaing the way the connectors are created), though, which
could perhaps be common code.

>> There are many custom applications using DRM directly and they assume that the
>> first connector is the 'main' display.
> 
> This is very unfortunate, but I still think it would be better to fix
> all those apps than patch kernel drivers one at a time to cater for
> user preferences with driver-specific kernel options.

I agree, but it's still a problem because we don't have access to those
apps. And they keep popping up when e.g. being used on a new platform
with multiple displays.

>> Afaik weston provides no means either to change the 'main/preferred' display.
> 
> Please, do not use Weston as justification for this. If you have window
> positioning problems in Weston, please come talk to us on #wayland or
> wayland-devel@, so we can discuss what you *actually* need.

Weston is just one piece of the puzzle. If Weston was the only problem,
then yes, we'd be working on Weston. But it's the combination of fbdev,
custom DRM based apps and Weston.

> Weston's behaviour in this respect has not been even defined yet, which
> makes a kernel option to work around it ever more awkward.
> 
> The reason why Weston lacks this kind of configurability is that no-one
> has needed it yet, I mean, come forth with a proposal, as far as I can
> recall. If people keep working around it elsewhere, it is unlikely Weston
> ever gets it.
> 
>> It should be the work of user space application (except the fb emulation) to
>> somehow deal with the 'main' display selection for their needs, but
>> unfortunately they are not capable of diong so for some reason.
> 
> Aside from Weston, which apps are these?

Mostly custom proprietary apps. But I think also Qt's DRM backend had
this problem, although I might remember wrong or it might have been
improved.

Overall, I don't like these module parameters much. But they did solve
issues our customers were having quite easily.

I am fine with dropping this from mainline, and just carrying it in the
TI kernel until we've come up with other solutions to the problems.

 Tomi

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