On 30/10/2024 3:12 pm, Leon Romanovsky wrote:
From: Christoph Hellwig <hch@xxxxxx>
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@xxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
---
include/linux/dma-mapping.h | 5 +++++
kernel/dma/mapping.c | 20 ++++++++++++++++++++
2 files changed, 25 insertions(+)
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 8074a3b5c807..6906edde505d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -410,6 +410,7 @@ 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)
{
@@ -435,6 +436,10 @@ 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 864a1121bf08..daa97a650778 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -442,6 +442,26 @@ 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.
In terms of the unmap call itself, why don't we just use dma_skip_sync
to short-cut dma_direct_unmap_*() and make sure it's as cheap as possible?
In terms of not having to unmap implying not having to store addresses
at all, it doesn't seem super-useful when you still have to store them
for long enough to find out that you don't :/
Thanks,
Robin.
+ */
+bool dma_need_unmap(struct device *dev)
+{
+ if (!dma_map_direct(dev, get_dma_ops(dev)))
+ return true;
+#ifdef CONFIG_DMA_NEED_SYNC
+ if (!dev->dma_skip_sync)
+ return true;
+#endif
+ 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);
