[PATCH v6 08/17] dma-mapping: add a dma_need_unmap helper

Leon Romanovsky
2025-01-17T11:18:08Z

From: Christoph Hellwig <hch@lst.de>

Add helper that allows a driver to skip calling dma_unmap_*
if the DMA layer can guarantee that they are no-nops.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
include/linux/dma-mapping.h | 5 +++++
kernel/dma/mapping.c | 18 ++++++++++++++++++
2 files changed, 23 insertions(+)

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index a71e110f1e9d..d2f358c5a25d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -406,6 +406,7 @@ static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
{
return dma_dev_need_sync(dev) ? __dma_need_sync(dev, dma_addr) : false;
}
+bool dma_need_unmap(struct device *dev);
#else /* !CONFIG_HAS_DMA || !CONFIG_DMA_NEED_SYNC */
static inline bool dma_dev_need_sync(const struct device *dev)
{
@@ -431,6 +432,10 @@ static inline bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
{
return false;
}
+static inline bool dma_need_unmap(struct device *dev)
+{
+ return false;
+}
#endif /* !CONFIG_HAS_DMA || !CONFIG_DMA_NEED_SYNC */

struct page *dma_alloc_pages(struct device *dev, size_t size,
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index cda127027e48..3c3204ad2839 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -443,6 +443,24 @@ bool __dma_need_sync(struct device *dev, dma_addr_t dma_addr)
}
EXPORT_SYMBOL_GPL(__dma_need_sync);

+/**
+ * dma_need_unmap - does this device need dma_unmap_* operations
+ * @dev: device to check
+ *
+ * If this function returns %false, drivers can skip calling dma_unmap_* after
+ * finishing an I/O. This function must be called after all mappings that might
+ * need to be unmapped have been performed.
+ */
+bool dma_need_unmap(struct device *dev)
+{
+ if (!dma_map_direct(dev, get_dma_ops(dev)))
+ return true;
+ if (!dev->dma_skip_sync)
+ return true;
+ return IS_ENABLED(CONFIG_DMA_API_DEBUG);
+}
+EXPORT_SYMBOL_GPL(dma_need_unmap);
+
static void dma_setup_need_sync(struct device *dev)
{
const struct dma_map_ops *ops = get_dma_ops(dev);
--
2.47.1