Am Donnerstag, den 26.02.2015, 12:44 +0900 schrieb Alexandre Courbot: > User-space use mappable BOs notably for fences, and expects that a > value update by the GPU will be immediatly visible through the > user-space mapping. > > ARM has a property that may prevent this from happening though: memory > can be mapped multiple times only if the different mappings share the > same caching properties. However all the lowmem memory is already > identity-mapped into the kernel with cache enabled, so when user-space > requests an uncached mapping, we actually get an "undefined caching > policy" one and this has strange side-effects described on Freedesktop > bug 86690. > > To prevent this from happening, allow user-space to explicitly specify > which objects should be coherent, and create such objects with the > TTM_PL_FLAG_UNCACHED flag. This will make TTM allocate memory using the > DMA API, which will fix the identify mapping and allow us to safely map > the objects to user-space uncached. > > Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx> Ok, this is only needed as userspace is skipping the cpu_prep for the fence BO reads. As doing this would increase the userspace fence overhead a lot, this flag seems to be the right thing to do. Reviewed-by: Lucas Stach <dev@xxxxxxxxxx> > --- > Patches that take advantage of this in Mesa will follow up shortly. I'd > to make sure the new flag is ok first before also adding it to libdrm. > > drm/nouveau/include/uapi/drm/nouveau_drm.h | 1 + > drm/nouveau/nouveau_gem.c | 3 +++ > 2 files changed, 4 insertions(+) > > diff --git a/drm/nouveau/include/uapi/drm/nouveau_drm.h b/drm/nouveau/include/uapi/drm/nouveau_drm.h > index 0d7608dc1a34..5507eead5863 100644 > --- a/drm/nouveau/include/uapi/drm/nouveau_drm.h > +++ b/drm/nouveau/include/uapi/drm/nouveau_drm.h > @@ -39,6 +39,7 @@ > #define NOUVEAU_GEM_DOMAIN_VRAM (1 << 1) > #define NOUVEAU_GEM_DOMAIN_GART (1 << 2) > #define NOUVEAU_GEM_DOMAIN_MAPPABLE (1 << 3) > +#define NOUVEAU_GEM_DOMAIN_COHERENT (1 << 4) > > #define NOUVEAU_GEM_TILE_COMP 0x00030000 /* nv50-only */ > #define NOUVEAU_GEM_TILE_LAYOUT_MASK 0x0000ff00 > diff --git a/drm/nouveau/nouveau_gem.c b/drm/nouveau/nouveau_gem.c > index 7c077fced1d1..0e690bf19fc9 100644 > --- a/drm/nouveau/nouveau_gem.c > +++ b/drm/nouveau/nouveau_gem.c > @@ -189,6 +189,9 @@ nouveau_gem_new(struct drm_device *dev, int size, int align, uint32_t domain, > if (!flags || domain & NOUVEAU_GEM_DOMAIN_CPU) > flags |= TTM_PL_FLAG_SYSTEM; > > + if (domain & NOUVEAU_GEM_DOMAIN_COHERENT) > + flags |= TTM_PL_FLAG_UNCACHED; > + > ret = nouveau_bo_new(dev, size, align, flags, tile_mode, > tile_flags, NULL, NULL, pnvbo); > if (ret) -- 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
