drm/ttm: Add a flag to allow drivers to skip clear-on-free

Add TTM_TT_FLAG_CLEARED_ON_FREE, which DRM drivers can set before
releasing backing stores if they want to skip clear-on-free.

Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Suggested-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240816135154.19678-1-nirmoy.das@intel.com
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>

drivers/gpu/drm/ttm/ttm_pool.c

@@ -222,15 +222,18 @@ static void ttm_pool_unmap(struct ttm_pool *pool, dma_addr_t dma_addr,
 }
 
 /* Give pages into a specific pool_type */
-static void ttm_pool_type_give(struct ttm_pool_type *pt, struct page *p)
+static void ttm_pool_type_give(struct ttm_pool_type *pt, struct page *p,
+			       bool cleared)
 {
 	unsigned int i, num_pages = 1 << pt->order;
 
-	for (i = 0; i < num_pages; ++i) {
-		if (PageHighMem(p))
-			clear_highpage(p + i);
-		else
-			clear_page(page_address(p + i));
+	if (!cleared) {
+		for (i = 0; i < num_pages; ++i) {
+			if (PageHighMem(p))
+				clear_highpage(p + i);
+			else
+				clear_page(page_address(p + i));
+		}
 	}
 
 	spin_lock(&pt->lock);
@@ -394,6 +397,7 @@ static void ttm_pool_free_range(struct ttm_pool *pool, struct ttm_tt *tt,
 				pgoff_t start_page, pgoff_t end_page)
 {
 	struct page **pages = &tt->pages[start_page];
+	bool cleared = tt->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE;
 	unsigned int order;
 	pgoff_t i, nr;
 
@@ -407,7 +411,7 @@ static void ttm_pool_free_range(struct ttm_pool *pool, struct ttm_tt *tt,
 
 		pt = ttm_pool_select_type(pool, caching, order);
 		if (pt)
-			ttm_pool_type_give(pt, *pages);
+			ttm_pool_type_give(pt, *pages, cleared);
 		else
 			ttm_pool_free_page(pool, caching, order, *pages);
 	}

include/drm/ttm/ttm_tt.h

@@ -85,6 +85,9 @@ struct ttm_tt {
 	 * fault handling abuses the DMA api a bit and dma_map_attrs can't be
 	 * used to assure pgprot always matches.
 	 *
+	 * TTM_TT_FLAG_CLEARED_ON_FREE: Set this if a drm driver handles
+	 * clearing backing store
+	 *
 	 * TTM_TT_FLAG_PRIV_POPULATED: TTM internal only. DO NOT USE. This is
 	 * set by TTM after ttm_tt_populate() has successfully returned, and is
 	 * then unset when TTM calls ttm_tt_unpopulate().
@@ -94,8 +97,9 @@ struct ttm_tt {
 #define TTM_TT_FLAG_EXTERNAL		BIT(2)
 #define TTM_TT_FLAG_EXTERNAL_MAPPABLE	BIT(3)
 #define TTM_TT_FLAG_DECRYPTED		BIT(4)
+#define TTM_TT_FLAG_CLEARED_ON_FREE	BIT(5)
 
-#define TTM_TT_FLAG_PRIV_POPULATED	BIT(5)
+#define TTM_TT_FLAG_PRIV_POPULATED	BIT(6)
 	uint32_t page_flags;
 	/** @num_pages: Number of pages in the page array. */
 	uint32_t num_pages;