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> --- 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) -- 2.3.0 -- 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
