在2024年6月29日六月 上午6:22，Icenowy Zheng写道：
[...]
> @@ -302,6 +302,10 @@ pgprot_t ttm_io_prot(struct ttm_buffer_object *bo,
> struct ttm_resource *res,
> caching = res->bus.caching;
> }
>
> + /* Downgrade cached mapping for non-snooping devices */
> + if (!bo->bdev->dma_coherent && caching == ttm_cached)
> + caching = ttm_write_combined;
Hi Icenowy,
Thanks for your patch! You saved many non-coh PCIe host implementations a day!.
Unfortunately I don't think we can safely ttm_cached to ttm_write_comnined, we've
had enough drama with write combine behaviour on all different platforms.
See drm_arch_can_wc_memory in drm_cache.h.
Thanks
> +
> return ttm_prot_from_caching(caching, tmp);
> }
> EXPORT_SYMBOL(ttm_io_prot);
> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> index 7b00ddf0ce49f..3335df45fba5e 100644
> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> @@ -152,6 +152,10 @@ static void ttm_tt_init_fields(struct ttm_tt *ttm,
> enum ttm_caching caching,
> unsigned long extra_pages)
> {
> + /* Downgrade cached mapping for non-snooping devices */
> + if (!bo->bdev->dma_coherent && caching == ttm_cached)
> + caching = ttm_write_combined;
> +
> ttm->num_pages = (PAGE_ALIGN(bo->base.size) >> PAGE_SHIFT) + extra_pages;
> ttm->page_flags = page_flags;
> ttm->dma_address = NULL;
> diff --git a/include/drm/ttm/ttm_caching.h b/include/drm/ttm/ttm_caching.h
> index a18f43e93abab..f92d7911f50e4 100644
> --- a/include/drm/ttm/ttm_caching.h
> +++ b/include/drm/ttm/ttm_caching.h
> @@ -47,7 +47,8 @@ enum ttm_caching {
>
> /**
> * @ttm_cached: Fully cached like normal system memory, requires that
> - * devices snoop the CPU cache on accesses.
> + * devices snoop the CPU cache on accesses. Downgraded to
> + * ttm_write_combined when the snooping capaiblity is missing.
> */
> ttm_cached
> };
> --
> 2.45.2
--
- Jiaxun
