EXA - when does it's implementation depend on DRM?

[Alex Deucher]

2010/7/4 Dave Airlie <airlied at gmail.com>:
> 2010/7/5 Rafał Miłecki <zajec5 at gmail.com>:
>> W dniu 4 lipca 2010 22:24 użytkownik Dave Airlie <airlied at gmail.com> napisał:
>>> 2010/7/5 Rafał Miłecki <zajec5 at gmail.com>:
>>>> AFAIU EXA is collection of operations (Solid, Copy, UploadToScreen,
>>>> DownloadFromScreen) that touch VRAM. So we can tell hardware to move
>>>> xterm window 100px right (Copy) and fill freed place with blue
>>>> (Solid). Is that right?
>>>>
>>>> So my question is: when implementing EXA (in DDX) needs DRM and when
>>>> it does not? I know in case of R6xx-R7xx we had to get DRM first to
>>>> receive EXA. AFAIK it wasn't the case with R1xx-R5xx.
>>>>
>>>> On the other hand some VIA's driver needs DRM for EXA on Chrome9,
>>>> while openChrome claims to support EXA without DRM[1].
>>>>
>>>> Could someone explain this to me, please?
>>>>
>>>> [1] http://phoronix.com/forums/showthread.php?p=89776
>>>
>>> Nothing to do with EXA, its up to the driver underneath.
>>
>> That's why I mentioned "implementation" in subject, not EXA itself :)
>>
>>
>>> If the driver can accel the operations without the drm, it doesn't
>>> need the drm, it the driver requires the drm to accel operations then
>>> it needs the drm
>>
>> Any tip why acceleration operations are available on some hardware
>> only with DRM, and sometimes not? Is this related to the way how we
>> send commands to GPU? AFAIK every command submission implementation
>> needs DRM... but somehow in case of r1xx-r5xx it is not true.
>
> You can program some GPUs via MMIO, its slower and you can't DMA
> to/from main memory at all, it just works in an offscreen memory area.
>
> Its generally pointless maintaining these codepaths since nobody tests
> them, and for chips like r600 I don't think MMIO is sufficient to
> program accel engines.

You can't program the r6xx+ 3D engines via MMIO directly.

>
> Not so sure on r500 its sufficient either since some regs can't be
> programmed via MMIO properly, but we have the codepaths since they are
> so similiar to r100.

Only copy and solid are available via mmio on r5xx since the
WAIT_UNTIL register and a few others are not accessible via MMIO.  In
theory even the 2D engine could be problematic without those regs, but
it's generally fairly well behaved.

Alex