On Thu, Dec 22, 2011 at 8:19 PM, James Simmons jsimmons@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