TTM and AGP conflicts

[Jerome Glisse]

On Fri, Dec 23, 2011 at 01:19:43AM +0000, James Simmons 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. 

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Attached is patch to fix this, so sorry about that, i must have lost my
agp change along the way when working on the patchset. This patch is not
extensively tested, i will do more testing tomorrow on more gpu, might
even found an nvidia agp i can try. Again sorry for breaking this.

Cheers,
Jerome