On Sun, Feb 2, 2014 at 10:43 PM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote: > On Sun, Feb 2, 2014 at 8:58 AM, Lucas Stach <dev@xxxxxxxxxx> wrote: >> Am Samstag, den 01.02.2014, 18:28 -0500 schrieb Ilia Mirkin: >>> On Sat, Feb 1, 2014 at 8:40 AM, Lucas Stach <dev@xxxxxxxxxx> wrote: >>> > Am Samstag, den 01.02.2014, 12:16 +0900 schrieb Alexandre Courbot: >>> >> Add a clumsy-but-working FB support for GK20A. This chip only uses system >>> >> memory, so we allocate a big chunk using CMA and let the existing memory >>> >> managers work on it. >>> >> >>> >> A better future design would be to allocate objects directly from system >>> >> memory without having to suffer from the limitations of a large, >>> >> contiguous pool. >>> >> >>> > I don't know if Tegra124 is similar to 114 in this regard [hint: get the >>> > TRM out :)], but if you go for a dedicated VRAM allocator, wouldn't it >>> > make sense to take a chunk of the MMIO overlaid memory for this when >>> > possible, rather than carving this out of CPU accessible mem? >>> >>> This is probably a stupid question... what do you need VRAM for >>> anyways? In _theory_ it's an abstraction to talk about memory that's >>> not accessible by the CPU. This is obviously not the case here, and >>> presumably the GPU can access all the memory in the system, so it can >>> be all treated as "GART" memory... AFAIK all accesses are behind the >>> in-GPU MMU, so contiguous physical memory isn't an issue either. In >>> practice, I suspect nouveau automatically sticks certain things into >>> vram (gpuobj's), but it should be feasible to make them optionally use >>> GART memory when VRAM is not available. I haven't really looked at the >>> details though, perhaps that's a major undertaking. >>> >>> -ilia >>> >> If it's similar to the Tegar114 there actually is memory that isn't >> accessible from the CPU. About 2GB of the address space is overlaid with >> MMIO for the devices, so in a 4GB system you potentially have 2GB of RAM >> that's only visible for the devices. >> >> But yes in general nouveau should just fall back to a GART placement if >> VRAM isn't available. > > With the limited time I spent studying it, it seems to me that Nouveau > has a strong dependency on VRAM. For gpuobjects indeed (that one could > be workarounded with a new instmem driver I suppose), and also for > TTM: objects placed in TTM_PL_VRAM are handled by the VRAM manager, > which requires a nouveau_ram instance in the FB. Actually the FB also > seems to assume the presence of a dedicated video RAM. > > So while I agree that getting rid of VRAM altogether would be the most > logical solution, I have not found a way to do so for the moment. > > T124's GPU actually sees the same physical address space as the CPU, > so memory management should be simplified thanks to that (you could > enable the SMMU and make things more interesting/complex, but for now > it seems untimely to even consider doing so). Actually even the > concept of a GART is not needed here: all your memory management needs > could be fulfilled by getting pages with alloc_page() and arranging > them using the GMMU. No GART, no BAR (at least for the purpose of > mapping objects for CPU access), no PRAMIN. So, looking at the code more closely I noticed the nouveau_ram::get() operation was only used by instmem (to allocate GPU objects) and TTM (for BOs in VRAM). I quickly wrote a custom instmem that allocates objects individually with dma_alloc_coherent() (and manually builds a nouveau_mem instance so they can be mapped into the BAR) and disabled nouveau_vram_manager for TTM, making TTM_PL_VRAM BOs use the GART manager. And oooh, it seems to work! :) I can remove that horrible CMA allocation and only keep the nouveau_ram instance as a dummy object providing 0MB of memory. I think this should be a viable solution, BOs never need to be contiguous thanks to the gMMU, and dma_alloc_coherent() returns contiguous memory for instobjs (not sure if *all* instobjs need to be contiguous in physical memory - page tables sure do - , but AFAICT we never allocate crazy-big instobjs). Any flaw/possible improvement with this design? Alex. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
