As we can now acquire the presence of the full DMA coherency (snooping
capability) from ttm_device, we can now map the CPU side memory as
write-combined when cached is requested and snooping is not avilable.
Signed-off-by: Icenowy Zheng <uwu@xxxxxxxxxx>
---
drivers/gpu/drm/ttm/ttm_bo_util.c | 4 ++++
drivers/gpu/drm/ttm/ttm_tt.c | 4 ++++
include/drm/ttm/ttm_caching.h | 3 ++-
3 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 0b3f4267130c4..6519ce047787d 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -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;
+
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
