Re: [RfC PATCH] drm: fourcc byteorder: brings header file comments in line with reality.

[Ilia Mirkin]

On Tue, Apr 11, 2017 at 3:31 AM, Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote:
> On Mon, 10 Apr 2017 12:10:14 -0400
> Ilia Mirkin <imirkin@xxxxxxxxxxxx> wrote:
>
>> On Mon, Apr 10, 2017 at 11:09 AM, Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote:
>
>> > I also wonder if a real BE machine could have different results than
>> > the virtual machine.
>>
>> I have a PPC G5 with an AGP GeForce FX 5200 that I can test things on,
>> if necessary. (I got it specifically for this purpose, as the people
>> who use this type of hw daily tend to perform updates rarely... in no
>> small part due to the fact that updates tend to break the HW.)
>>
>> Just let know what you need tested, I should be able to turn it around
>> within a couple of days.
>
> That's part of my problem. I don't really know what should be tested.
> What do people do with their BE machines that we should avoid breaking?
>
> I suppose correlating with what Gerd was testing would be nice, i.e.
> does X.org with modesetting look right with and without GLAMOR? Maybe
> you also want to throw in xf86-video-nouveau for comparison.

GLAMOR? That's funny. No way that works. Pretty sure it doesn't work
on nv30/nv40 GPUs on LE boxes (at least I get bugs about it). I've
gotten mesa to the point where simple demos work again (after it got
"fixed" for BE, thus breaking all previously working setups). However
there's too much confusion in my head about how to store buffer data,
and precisely what the "BE" mode on the GPUs does for anything complex
to work.

> As to what apps to test those with... Gerd? I presume anything that does
> *not* use OpenGL, since we have doubts of Mesa's correctness on BE,
> right? So maybe some of the traditional ancient X11 apps? xterm with
> colours?

Mesa's fine on BE again, at least the nv30 driver. I had to do some
slightly dubious things to get it to that state, but it does function
mostly properly (as long as you don't try to use VBOs ... or index
buffers ... something ends up getting byteswapped one too many times,
however that's a wholly nv30-private issue).

> However, I totally agree with Alex that someone with a BE machine
> should review the whole stack before we could be confident with anything.

Here's what I'm confident about: xf86-video-nouveau worked just fine
on top of kernel 4.3 on an AGP GeForce FX 5200 (with AGPGART turned
off because ... well ... uninorth). fbcon/fbdev accel worked,
xf86-video-nouveau's 2d accel worked, and simple demos (ala glxgears)
worked after I fixed up mesa and nv30 driver items in version ... 11.1
it seems. As I recall it had gotten all broken in 10.0 or so by Adam
Jackson in the name of making llvmpipe work on BE, declaring all other
drivers broken, with various fixes by Michel DÃnzer to get it back to
working over the years.

Anyone "fixing" the stack has to maintain that level of functioning
through their various fixing.

I will double-check that the above still works with the latest
kernel/xorg/xf86-video-nouveau/mesa and report back (hopefully by this
weekend). If there are any patches you'd like me to test, now's the
time to ask -- getting the box up and running is the hard part,
booting up an extra kernel -- easy.

Cheers,

  -ilia