[PATCH] drm/radeon: TTM must be init with cpu-visible VRAM

[Christian König]

Am 28.02.2014 16:36, schrieb Lauri Kasanen:
> On Fri, 28 Feb 2014 17:30:39 +0200
> Lauri Kasanen <cand at gmx.com> wrote:
>
>> On Fri, 28 Feb 2014 10:36:59 +0100
>> Christian König <deathsimple at vodafone.de> wrote:
>>
>>> Am 27.02.2014 22:38, schrieb Lauri Kasanen:
>>>> Without this, a bo may get created in the cpu-inaccessible vram.
>>>> Before the CP engines get setup, all copies are done via cpu memcpy.
>>>>
>>>> This means that the cpu tries to read from inaccessible memory, fails,
>>>> and the radeon module proceeds to disable acceleration.
>>>>
>>>> Doing this has no downsides, as the real VRAM size gets set as soon as the
>>>> CP engines get init.
>>>>
>>>> This is a candidate for 3.14 fixes.
>>> This should be unnecessary, since TTM gets initialized only seeing the
>>> visible VRAM and later on radeon_ttm_set_active_vram_size gets called to
>>> increase the limit.
>>>
>>> If this isn't the case any more we should figure out why instead of
>>> working around it like this.
>> Negative, TTM gets initialized with real_vram just a few lines above
>> this patch, not visible_vram.
> git blame shows 7a50f01a from 2009, "drm/radeon/kms: vram sizing on
> certain r100 chips needs workaround." by Dave Airlie.
>
> So the TTM VRAM init has been wrong for five years, and only worked by
> accident because until now all allocations were done bottom-up.

Yeah, just came to the same conclusion. We probably never hit the case 
in the last five years because we don't really access the memory before 
we start the copy ring.

Please fix ttm_bo_init_mm to use rdev->mc.visible_vram_size instead.

That allocations are made bottom-up is relied upon in a couple of other 
cases as well, the stolen VGA memory and the UVD firmware handling for 
example.

Christian.

> - Lauri