[PATCH RFC 2/8] DRM: Armada: Add Armada DRM driver

[Rob Clark]

On Wed, Jun 12, 2013 at 9:48 AM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Tue, Jun 11, 2013 at 09:48:57AM +1000, Dave Airlie wrote:
>> On Tue, Jun 11, 2013 at 9:36 AM, Russell King - ARM Linux
>> <linux at arm.linux.org.uk> wrote:
>> > On Tue, Jun 11, 2013 at 09:24:16AM +1000, Dave Airlie wrote:
>> >> I'd like to see all the ARM based drivers based on CMA if it can meet
>> >> their requirements
>> >> and using close to standard GEM/dma-buf interfaces. Otherwise it'll be
>> >> come an unmaintainable
>> >> nightmare for everyone, but mostly for me.
>> >
>> > I am *not* using the CMA layer - that layer is just plain broken in
>> > DRM.  It forces every single gem object to be a CMA allocated object,
>> > which means I can't have cacheable pixmaps in X.  And that makes X
>> > suck.
>> >
>> > Okay, I'm pulling this and I'm going to keep it in my private cubox
>> > tree; I'm not persuing pushing this driver or any other Armada 510
>> > driver into mainline anymore.  It's just too much fscking hastle
>> > dealing with people who don't like various stuff.
>> >
>> > I've done my best to clean a lot of the crap up, and the problem is
>> > that no matter how much I clean up, it remains unacceptable.  Only
>> > the 100% perfect solution seems to be acceptable.  That is
>> > unacceptable given that this stuff has already consumed something
>> > like 8 months solid of my time.
>>
>> Russell, aren't you a kernel maintainer, because for fuck sake get real.
>>
>> I'm not merging bullshit into my tree that has a completely broken API that
>> has to be maintained for ever. You of all people should understand we
>> don't break Linux
>> userspace APIs, and adding a phys addr one is wrong, wrong, wrong, its not
>> cleanups, its just broken, and I'll never merge it.
>
> And having thought about this driver, DRM some more, I'm now of the
> opinion that DRM is not suitable for driving hardware where the GPU is
> an entirely separate IP block from the display side.
>
> DRM is modelled after the PC setup where your "graphics card" does
> everything - it has the GPU, display and connectors all integrated
> together.  This is not the case on embedded SoCs, which can be a
> collection of different IPs all integrated together.

actually it isn't even the case on desktop/laptop anymore, where you
can have one gpu with scanout and a second one without (or just with
display controller not hooked up to anything, etc, etc)

That is the point of dmabuf and the upcoming fence/reservation stuff.

BR,
-R

> DRM is based on the assumption that you have a single card and everything
> is known about that card.  Again, this is not the case with embedded SoCs,
> which is why Sebastian is having a hard time with the DRM slave encoder
> stuff.
>
> If DRM is going to be usable on SoCs, it needs to become more modular in
> nature, allowing the same scanout stuff to be used with different GPUs
> and providing _kernel_ side interfaces to allow different GPUs to be
> plugged in to a scanout implementation, or vice versa (the reverse is
> probably easier because the scanout interface is nicely abstracted).
>
> Or we go off and write an entirely new subsystem which *does* suit the
> needs of modular SoC implementations.