Re: [RFC PATCH 3/5] drm/ttm: Use drm_memcpy_from_wc for TTM bo moves

["Christian König" <christian.koenig@amd.com>]

Am 20.05.21 um 17:09 schrieb Thomas Hellström:
> Use fast wc memcpy for reading out of wc memory for TTM bo moves.
>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

Oh, yes I really wanted to have that in TTM for quite some time.

But I'm wondering if we shouldn't fix the memremap stuff first.

Christian.

> ---
>   drivers/gpu/drm/ttm/ttm_bo_util.c | 18 +++++++++++++++++-
>   1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index bad9b16e96ba..919ee03f7eb3 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -31,6 +31,7 @@
>   
>   #include <drm/ttm/ttm_bo_driver.h>
>   #include <drm/ttm/ttm_placement.h>
> +#include <drm/drm_memcpy.h>
>   #include <drm/drm_vma_manager.h>
>   #include <linux/dma-buf-map.h>
>   #include <linux/io.h>
> @@ -185,6 +186,7 @@ void ttm_move_memcpy(struct ttm_buffer_object *bo,
>   	struct ttm_resource *old_mem = &bo->mem;
>   	struct ttm_resource_manager *old_man = ttm_manager_type(bdev, old_mem->mem_type);
>   	struct dma_buf_map old_map, new_map;
> +	bool wc_memcpy;
>   	pgoff_t i;
>   
>   	/* Single TTM move. NOP */
> @@ -208,11 +210,25 @@ void ttm_move_memcpy(struct ttm_buffer_object *bo,
>   		return;
>   	}
>   
> +	wc_memcpy = ((!old_man->use_tt || bo->ttm->caching != ttm_cached) &&
> +		     drm_has_memcpy_from_wc());
> +
> +	/*
> +	 * We use some nasty aliasing for drm_memcpy_from_wc, but assuming
> +	 * that we can move to memremapping in the not too distant future,
> +	 * reduce the fragility for now with a build assert.
> +	 */
> +	BUILD_BUG_ON(offsetof(typeof(old_map), vaddr) !=
> +		     offsetof(typeof(old_map), vaddr_iomem));
> +
>   	for (i = 0; i < new_mem->num_pages; ++i) {
>   		new_iter->ops->kmap_local(new_iter, &new_map, i);
>   		old_iter->ops->kmap_local(old_iter, &old_map, i);
>   
> -		if (!old_map.is_iomem && !new_map.is_iomem) {
> +		if (wc_memcpy) {
> +			drm_memcpy_from_wc(new_map.vaddr, old_map.vaddr,
> +					   PAGE_SIZE);
> +		} else if (!old_map.is_iomem && !new_map.is_iomem) {
>   			memcpy(new_map.vaddr, old_map.vaddr, PAGE_SIZE);
>   		} else if (!old_map.is_iomem) {
>   			dma_buf_map_memcpy_to(&new_map, old_map.vaddr,