[RFC v2 0/5] Common Display Framework

[Rob Clark]

On Mon, Dec 17, 2012 at 11:04 PM, Dave Airlie <airlied at gmail.com> wrote:
>>
>> Many developers showed interest in the first RFC, and I've had the opportunity
>> to discuss it with most of them. I would like to thank (in no particular
>> order) Tomi Valkeinen for all the time he spend helping me to draft v2, Marcus
>> Lorentzon for his useful input during Linaro Connect Q4 2012, and Linaro for
>> inviting me to Connect and providing a venue to discuss this topic.
>>
>
> So this might be a bit off topic but this whole CDF triggered me
> looking at stuff I generally avoid:
>
> The biggest problem I'm having currently with the whole ARM graphics
> and output world is the proliferation of platform drivers for every
> little thing. The whole ordering of operations with respect to things
> like suspend/resume or dynamic power management is going to be a real
> nightmare if there are dependencies between the drivers. How do you
> enforce ordering of s/r operations between all the various components?

I tend to think that sub-devices are useful just to have a way to
probe hw which may or may not be there, since on ARM we often don't
have any alternative.. but beyond that, suspend/resume, and other
life-cycle aspects, they should really be treated as all one device.
Especially to avoid undefined suspend/resume ordering.

CDF or some sort of mechanism to share panel drivers between drivers
is useful.  Keeping it within drm, is probably a good idea, if nothing
else to simplify re-use of helper fxns (like avi-infoframe stuff, for
example) and avoid dealing with merging changes across multiple trees.
  Treating them more like shared libraries and less like sub-devices
which can be dynamically loaded/unloaded (ie. they should be not built
as separate modules or suspend/resumed or probed/removed independently
of the master driver) is a really good idea to avoid uncovering nasty
synchronization issues later (remove vs modeset or pageflip) or
surprising userspace in bad ways.

> The other thing I'd like you guys to do is kill the idea of fbdev and
> v4l drivers that are "shared" with the drm codebase, really just
> implement fbdev and v4l on top of the drm layer, some people might
> think this is some sort of maintainer thing, but really nothing else
> makes sense, and having these shared display frameworks just to avoid
> having using drm/kms drivers seems totally pointless. Fix the drm
> fbdev emulation if an fbdev interface is needed. But creating a fourth
> framework because our previous 3 frameworks didn't work out doesn't
> seem like a situation I want to get behind too much.

yeah, let's not have multiple frameworks to do the same thing.. For
fbdev, it is pretty clear that it is a dead end.  For v4l2
(subdev+mcf), it is perhaps bit more flexible when it comes to random
arbitrary hw pipelines than kms.  But to take advantage of that, your
userspace isn't going to be portable anyways, so you might as well use
driver specific properties/ioctls.  But I tend to think that is more
useful for cameras.  And from userspace perspective, kms planes are
less painful to use for output than v4l2, so lets stick to drm/kms for
output (and not try to add camera/capture support to kms).. k, thx

BR,
-R

> Dave.
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