Am Freitag, den 23.05.2014, 16:10 +0900 schrieb Alexandre Courbot: > On Mon, May 19, 2014 at 7:16 PM, Lucas Stach <l.stach@xxxxxxxxxxxxxx> wrote: > > Am Montag, den 19.05.2014, 19:06 +0900 schrieb Alexandre Courbot: > >> On 05/19/2014 06:57 PM, Lucas Stach wrote: > >> > Am Montag, den 19.05.2014, 18:46 +0900 schrieb Alexandre Courbot: > >> >> This patch is not meant to be merged, but rather to try and understand > >> >> why this is needed and what a more suitable solution could be. > >> >> > >> >> Allowing BOs to be write-cached results in the following happening when > >> >> trying to run any program on Tegra/GK20A: > >> >> > >> >> Unhandled fault: external abort on non-linefetch (0x1008) at 0xf0036010 > >> >> ... > >> >> (nouveau_bo_rd32) from [<c0357d00>] (nouveau_fence_update+0x5c/0x80) > >> >> (nouveau_fence_update) from [<c0357d40>] (nouveau_fence_done+0x1c/0x38) > >> >> (nouveau_fence_done) from [<c02c3d00>] (ttm_bo_wait+0xec/0x168) > >> >> (ttm_bo_wait) from [<c035e334>] (nouveau_gem_ioctl_cpu_prep+0x44/0x100) > >> >> (nouveau_gem_ioctl_cpu_prep) from [<c02aaa84>] (drm_ioctl+0x1d8/0x4f4) > >> >> (drm_ioctl) from [<c0355394>] (nouveau_drm_ioctl+0x54/0x80) > >> >> (nouveau_drm_ioctl) from [<c00ee7b0>] (do_vfs_ioctl+0x3dc/0x5a0) > >> >> (do_vfs_ioctl) from [<c00ee9a8>] (SyS_ioctl+0x34/0x5c) > >> >> (SyS_ioctl) from [<c000e6e0>] (ret_fast_syscall+0x0/0x30 > >> >> > >> >> The offending nouveau_bo_rd32 is done over an IO-mapped BO, e.g. a BO > >> >> mapped through the BAR. > >> >> > >> > Um wait, this memory is behind an already mapped bar? I think ioremap on > >> > ARM defaults to uncached mappings, so if you want to access the memory > >> > behind this bar as WC you need to map the BAR as a whole as WC by using > >> > ioremap_wc. > >> > >> Tried mapping the BAR using ioremap_wc(), but to no avail. On the other > >> hand, could it be that VRAM BOs end up creating a mapping over an > >> already-mapped region? I seem to remember that ARM might not like it... > > > > Multiple mapping are generally allowed, as long as they have the same > > caching state. It's conflicting mappings (uncached vs cached, or cached > > vs wc), that are documented to yield undefined results. > > Sorry about the confusion. The BAR is *not* mapped to the kernel yet > (it is BAR1, there is no BAR3 on GK20A) and an ioremap_*() is > performed in ttm_bo_ioremap() to make the part of the BAR where the > buffer is mapped visible. It seems that doing an ioremap_wc() on the > BAR area on Tegra is what leads to these errors. ioremap() or > ioremap_nocache() (which are in effect the same on ARM) do not cause > this issue. > It would be cool if you could ask HW, or the blob developers, if this is a general issue. The external abort is clearly the GPUs AXI client responding with an error to the read request, though I'm not clear where a WC read differs from an uncached one. > The best way to solve this issue would be to not use the BAR at all > since the memory behind these objects can be directly accessed by the > CPU. As such it would better be mapped using ttm_bo_kmap_ttm() > instead. But right now this is clearly not how nouveau_bo.c is written > and it does not look like this can easily be done. :/ Yeah, it sounds like we want this shortcut for stolen VRAM implementations. Regards, Lucas -- Pengutronix e.K. | Lucas Stach | Industrial Linux Solutions | http://www.pengutronix.de/ | -- 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
