[PATCH net-next v5 08/14] page_pool: add DMA-sync-for-CPU inline helpers

[Alexander Lobakin]

Each driver is responsible for syncing buffers written by HW for CPU
before accessing them. Almost each PP-enabled driver uses the same
pattern, which could be shorthanded into a static inline to make driver
code a little bit more compact.
Introduce a couple such functions. The first one is sorta internal and
performs DMA synchronization unconditionally for the size passed from
the driver. The second checks whether the synchronization is needed
for this pool first and is the main one to be used by the drivers.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
---
 include/net/page_pool/helpers.h | 43 +++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 528a76c66270..797275e75d38 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h
@@ -432,6 +432,49 @@ static inline bool page_pool_dma_addr_need_sync(const struct page *page)
 	return page->dma_addr & PAGE_POOL_DMA_ADDR_NEED_SYNC;
 }
 
+/**
+ * __page_pool_dma_sync_for_cpu - sync Rx page for CPU after it's written by HW
+ * @pool: &page_pool the @page belongs to
+ * @page: page to sync
+ * @offset: offset from page start to "hard" start if using frags
+ * @dma_sync_size: size of the data written to the page
+ *
+ * Can be used as a shorthand to sync Rx pages before accessing them in the
+ * driver. Caller must ensure the pool was created with ```PP_FLAG_DMA_MAP```.
+ * Note that this version performs DMA sync unconditionally, even if the
+ * associated PP doesn't perform sync-for-device. Consider the non-underscored
+ * version first if unsure.
+ */
+static inline void __page_pool_dma_sync_for_cpu(const struct page_pool *pool,
+						const struct page *page,
+						u32 offset, u32 dma_sync_size)
+{
+	dma_sync_single_range_for_cpu(pool->p.dev,
+				      page_pool_get_dma_addr(page),
+				      offset + pool->p.offset, dma_sync_size,
+				      page_pool_get_dma_dir(pool));
+}
+
+/**
+ * page_pool_dma_sync_for_cpu - sync Rx page for CPU if needed
+ * @pool: &page_pool the @page belongs to
+ * @page: page to sync
+ * @offset: offset from page start to "hard" start if using frags
+ * @dma_sync_size: size of the data written to the page
+ *
+ * Performs DMA sync for CPU, but *only* when both:
+ * 1) page_pool was created with ```PP_FLAG_DMA_SYNC_DEV``` to manage DMA sync;
+ * 2) sync shortcut is not available (IOMMU, swiotlb, non-coherent DMA, ...)
+ */
+static inline void page_pool_dma_sync_for_cpu(const struct page_pool *pool,
+					      const struct page *page,
+					      u32 offset, u32 dma_sync_size)
+{
+	if (page_pool_dma_addr_need_sync(page))
+		__page_pool_dma_sync_for_cpu(pool, page, offset,
+					     dma_sync_size);
+}
+
 static inline bool page_pool_put(struct page_pool *pool)
 {
 	return refcount_dec_and_test(&pool->user_cnt);
-- 
2.42.0