In ttm_bo_vmap(), set up single-page mappings with kmap() in certain cases. The feature is already present in ttm_bo_kmap().
This functionality is require by DRM's xe driver, which claims that using kmap() is an optimization over vmap(). [1] Reading the commit at [2] indicates otherwise. It is not possible to use kmap_local_page() and kunmap_local_page(), as TTM cannot guarantee the requirements for ordering these calls. [3] Signed-off-by: Thomas Zimmermann <[email protected]> Link: https://elixir.bootlin.com/linux/v6.9/source/drivers/gpu/drm/xe/xe_bo.c#L1870 # 1 Link: https://lore.kernel.org/all/[email protected]/T/#u # 2 Link: https://elixir.bootlin.com/linux/v6.9/source/include/linux/highmem.h#L70 # 3 --- drivers/gpu/drm/ttm/ttm_bo_util.c | 33 ++++++++++++++++++++++--------- 1 file changed, 24 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c index 31f9772f05dac..c06cfccace39d 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_util.c +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c @@ -516,6 +516,8 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, .no_wait_gpu = false }; struct ttm_tt *ttm = bo->ttm; + struct ttm_resource_manager *man = + ttm_manager_type(bo->bdev, bo->resource->mem_type); unsigned long start_page = offset >> PAGE_SHIFT; unsigned long aligned_size = size + (offset - (start_page << PAGE_SHIFT)); unsigned long num_pages = DIV_ROUND_UP(aligned_size, PAGE_SIZE); @@ -527,15 +529,25 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, if (ret) return ret; - /* - * We need to use vmap to get the desired page protection - * or to make the buffer object look contiguous. - */ - prot = ttm_io_prot(bo, mem, PAGE_KERNEL); - vaddr = vmap(ttm->pages + start_page, num_pages, 0, prot); - if (!vaddr) - return -ENOMEM; - alloc_flags = ttm_bo_map_vmap; + if (num_pages == 1 && ttm->caching == ttm_cached && + !(man->use_tt && (ttm->page_flags & TTM_TT_FLAG_DECRYPTED))) { + /* + * We're mapping a single page, and the desired + * page protection is consistent with the bo. + */ + vaddr = kmap(ttm->pages[start_page]); + alloc_flags = ttm_bo_map_kmap; + } else { + /* + * We need to use vmap to get the desired page protection + * or to make the buffer object look contiguous. + */ + prot = ttm_io_prot(bo, mem, PAGE_KERNEL); + vaddr = vmap(ttm->pages + start_page, num_pages, 0, prot); + if (!vaddr) + return -ENOMEM; + alloc_flags = ttm_bo_map_vmap; + } iosys_map_set_vaddr(map, vaddr); map->alloc_flags = alloc_flags; @@ -567,6 +579,9 @@ void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct iosys_map *map) case ttm_bo_map_vmap: vunmap(map->vaddr); break; + case ttm_bo_map_kmap: + kunmap(kmap_to_page(map->vaddr)); + break; case ttm_bo_map_premapped: break; default: -- 2.45.2
