TTM and AGP conflicts

[Jerome Glisse]

On Thu, Dec 22, 2011 at 8:19 PM, James Simmons <jsimmons at infradead.org> wrote:
>
>> > Hi!
>> >
>> >        I updated the openchrome tree and while testing on the AGP system
>> > discovered some interesting problems with the new TTM changes. The
>> > problems center around the ttm_tt_[un]populate which I modeled after the
>> > radeon and nouveau driver.
>> >        First problem I noticed was on a AGP system that my ttm_tt_populate
>> > function would oops. Tracking it down I found the problem was the
>> > ttm_agp_tt_create calls ttm_tt_init instead of ttm_dma_tt_init so once my
>> > ttm_tt_populate function would attempt to touch the dma_address it would
>> > oops. The second issue is the assumption of the cast for struct ttm_tt in
>> > both the populate and unpopulate function. For the AGP case the proper
>> > case would be to ttm_agp_backend.
>> >        At this point my assumption is the ttm_bo_move function has to be
>> > rewritten to handle the AGP case to avoid calling ttm_tt_bind and in all
>> > cases ttm_tt_bind needs to be avoided. Looking at the radeon and nouveau
>> > drivers I don't see that testing happening. Am I just missing something?
>>
>> Happens on AGP radeons as well:
>> https://bugs.freedesktop.org/show_bug.cgi?id=43719
>
>        So I'm not crazy, so this needs to be fixed. Here is what my
> understanding of the TTM layer is. My impression is that struct ttm_bo_driver
> handles multiple domains, AGP, pcie etc and in each method you have to
> handle each specific domain you support. Also *move gives the impression of
> moving between these different domains.
>        Where as for struct ttm_backend_func was more for allocating from
> a specific domain. Also I never saw a clear way to handle multiple backends.
> For example my AGP systems can also do pci dma as well.

Yes this need to be fixed, i am likely guilty, i tested agp along the
way but i must have miss something. If no one beat me to it i will get
back to this on january.

Cheers,
Jerome