linux-kernel - [PATCH v6 08/17] dma-mapping: add a dma_need

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Message-ID: <9458f681274f4f0e5dd3bf3959e0b8a1ac9a4e7b.1737106761.git.leon@kernel.org>
Date: Fri, 17 Jan 2025 12:03:39 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Christoph Hellwig <hch@....de>,
	Jason Gunthorpe <jgg@...pe.ca>,
	Robin Murphy <robin.murphy@....com>
Cc: Jens Axboe <axboe@...nel.dk>,
	Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Sagi Grimberg <sagi@...mberg.me>,
	"Keith Busch" <kbusch@...nel.org>,
	"Bjorn Helgaas" <bhelgaas@...gle.com>,
	"Logan Gunthorpe" <logang@...tatee.com>,
	"Yishai Hadas" <yishaih@...dia.com>,
	"Shameer Kolothum" <shameerali.kolothum.thodi@...wei.com>,
	"Kevin Tian" <kevin.tian@...el.com>,
	"Alex Williamson" <alex.williamson@...hat.com>,
	"Marek Szyprowski" <m.szyprowski@...sung.com>,
	Jérôme Glisse <jglisse@...hat.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Jonathan Corbet" <corbet@....net>,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org,
	linux-rdma@...r.kernel.org,
	iommu@...ts.linux.dev,
	linux-nvme@...ts.infradead.org,
	linux-pci@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-mm@...ck.org,
	"Randy Dunlap" <rdunlap@...radead.org>
Subject: [PATCH v6 08/17] dma-mapping: add a dma_need_unmap helper

From: Christoph Hellwig <hch@....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@....de>
Signed-off-by: Leon Romanovsky <leonro@...dia.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