[PATCH v2 02/33] drm/ttm/pool: Add ttm_pool_page_order_nodma() helper

[Matthew Brost]

TTM records the allocation order of a multi-order page in page->private at
allocation time. For pools that do not use dma_alloc the order is stored
directly, while dma_alloc pools store a struct ttm_pool_dma pointer there
instead. Drivers that do their own DMA mapping (e.g. Xe) need the per-page
order to walk a populated ttm_tt one chunk at a time, but cannot rely on
folio_order(): TTM allocates high-order pages with alloc_pages_node()
without __GFP_COMP, so they are not compound and folio_order() always
returns 0.

Expose ttm_pool_page_order_nodma(), a thin wrapper that returns the order
recorded in page->private. It is only valid for pages from a pool that does
not use dma_alloc; whether a TTM device uses dma_alloc is fixed at ttm
device init time, so callers know from their device configuration that this
helper applies. Use it from the existing internal ttm_pool_page_order() to
keep a single source of truth.

Cc: Carlos Santa <carlos.santa@xxxxxxxxx>
Cc: Ryan Neph <ryanneph@xxxxxxxxxx>
Cc: Christian Koenig <christian.koenig@xxxxxxx>
Cc: Huang Rui <ray.huang@xxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Cc: Maxime Ripard <mripard@xxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Simona Vetter <simona@xxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
Assisted-by: GitHub_Copilot:claude-opus-4.8
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
 drivers/gpu/drm/ttm/ttm_pool.c | 25 ++++++++++++++++++++++++-
 include/drm/ttm/ttm_pool.h     |  2 ++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
index dbe977412a81..d34592d4dbc7 100644
--- a/drivers/gpu/drm/ttm/ttm_pool.c
+++ b/drivers/gpu/drm/ttm/ttm_pool.c
@@ -461,6 +461,29 @@ static unsigned int ttm_pool_shrink(int nid, unsigned long num_to_free)
 	return num_pages;
 }
 
+/**
+ * ttm_pool_page_order_nodma() - Allocation order of a non-dma_alloc TTM page
+ * @p: The page to query.
+ *
+ * Return the allocation order that the TTM pool allocator recorded in
+ * @p->private at allocation time. This only works for pages that were
+ * allocated from a pool which does *not* use dma_alloc (i.e. pages backed by
+ * alloc_pages_node()), where TTM stores the order directly in page->private.
+ *
+ * For dma_alloc pools, page->private instead holds a struct ttm_pool_dma
+ * pointer and this helper must not be used. Whether a TTM device uses
+ * dma_alloc is fixed at ttm device init time, so callers are expected to know
+ * from their TTM device configuration that their pages are not dma_alloc
+ * backed before using this helper.
+ *
+ * Return: The allocation order of the page.
+ */
+unsigned int ttm_pool_page_order_nodma(struct page *p)
+{
+	return p->private;
+}
+EXPORT_SYMBOL(ttm_pool_page_order_nodma);
+
 /* Return the allocation order based for a page */
 static unsigned int ttm_pool_page_order(struct ttm_pool *pool, struct page *p)
 {
@@ -470,7 +493,7 @@ static unsigned int ttm_pool_page_order(struct ttm_pool *pool, struct page *p)
 		return dma->vaddr & ~PAGE_MASK;
 	}
 
-	return p->private;
+	return ttm_pool_page_order_nodma(p);
 }
 
 /*
diff --git a/include/drm/ttm/ttm_pool.h b/include/drm/ttm/ttm_pool.h
index 26ee592e1994..753203980e2c 100644
--- a/include/drm/ttm/ttm_pool.h
+++ b/include/drm/ttm/ttm_pool.h
@@ -94,6 +94,8 @@ long ttm_pool_backup(struct ttm_pool *pool, struct ttm_tt *ttm,
 int ttm_pool_restore_and_alloc(struct ttm_pool *pool, struct ttm_tt *tt,
 			       const struct ttm_operation_ctx *ctx);
 
+unsigned int ttm_pool_page_order_nodma(struct page *p);
+
 int ttm_pool_mgr_init(unsigned long num_pages);
 void ttm_pool_mgr_fini(void);
 
-- 
2.34.1