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[kernel,v4,1/2] dma: Allow mixing bypass and mapped DMA operation

Message ID 20201029015241.73920-2-aik@ozlabs.ru
State Not Applicable
Headers show
Series DMA, powerpc/dma: Fallback to dma_ops when persistent memory present | expand


Context Check Description
snowpatch_ozlabs/needsstable success Patch has no Fixes tags
snowpatch_ozlabs/checkpatch success
snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (8cb17737940b156329cb5210669b9c9b23f4dd56)

Commit Message

Alexey Kardashevskiy Oct. 29, 2020, 1:52 a.m. UTC
At the moment we allow bypassing DMA ops only when we can do this for
the entire RAM. However there are configs with mixed type memory
where we could still allow bypassing IOMMU in most cases;
POWERPC with persistent memory is one example.

This adds an arch hook to determine where bypass can still work and
we invoke direct DMA API. The following patch checks the bus limit
on POWERPC to allow or disallow direct mapping.

This adds a CONFIG_ARCH_HAS_DMA_SET_MASK config option to make arch_xxxx
hooks no-op by default.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
* wrapped long lines
 kernel/dma/mapping.c | 26 ++++++++++++++++++++++----
 kernel/dma/Kconfig   |  4 ++++
 2 files changed, 26 insertions(+), 4 deletions(-)
diff mbox series


diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 51bb8fa8eb89..ad1f052e046d 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -137,6 +137,20 @@  static inline bool dma_map_direct(struct device *dev,
 	return dma_go_direct(dev, *dev->dma_mask, ops);
+bool arch_dma_map_page_direct(struct device *dev, phys_addr_t addr);
+bool arch_dma_unmap_page_direct(struct device *dev, dma_addr_t dma_handle);
+bool arch_dma_map_sg_direct(struct device *dev, struct scatterlist *sg,
+			    int nents);
+bool arch_dma_unmap_sg_direct(struct device *dev, struct scatterlist *sg,
+			      int nents);
+#define arch_dma_map_page_direct(d, a) (0)
+#define arch_dma_unmap_page_direct(d, a) (0)
+#define arch_dma_map_sg_direct(d, s, n) (0)
+#define arch_dma_unmap_sg_direct(d, s, n) (0)
 dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
 		size_t offset, size_t size, enum dma_data_direction dir,
 		unsigned long attrs)
@@ -149,7 +163,8 @@  dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
 	if (WARN_ON_ONCE(!dev->dma_mask))
-	if (dma_map_direct(dev, ops))
+	if (dma_map_direct(dev, ops) ||
+	    arch_dma_map_page_direct(dev, page_to_phys(page) + offset + size))
 		addr = dma_direct_map_page(dev, page, offset, size, dir, attrs);
 		addr = ops->map_page(dev, page, offset, size, dir, attrs);
@@ -165,7 +180,8 @@  void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
 	const struct dma_map_ops *ops = get_dma_ops(dev);
-	if (dma_map_direct(dev, ops))
+	if (dma_map_direct(dev, ops) ||
+	    arch_dma_unmap_page_direct(dev, addr + size))
 		dma_direct_unmap_page(dev, addr, size, dir, attrs);
 	else if (ops->unmap_page)
 		ops->unmap_page(dev, addr, size, dir, attrs);
@@ -188,7 +204,8 @@  int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
 	if (WARN_ON_ONCE(!dev->dma_mask))
 		return 0;
-	if (dma_map_direct(dev, ops))
+	if (dma_map_direct(dev, ops) ||
+	    arch_dma_map_sg_direct(dev, sg, nents))
 		ents = dma_direct_map_sg(dev, sg, nents, dir, attrs);
 		ents = ops->map_sg(dev, sg, nents, dir, attrs);
@@ -207,7 +224,8 @@  void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,
 	debug_dma_unmap_sg(dev, sg, nents, dir);
-	if (dma_map_direct(dev, ops))
+	if (dma_map_direct(dev, ops) ||
+	    arch_dma_unmap_sg_direct(dev, sg, nents))
 		dma_direct_unmap_sg(dev, sg, nents, dir, attrs);
 	else if (ops->unmap_sg)
 		ops->unmap_sg(dev, sg, nents, dir, attrs);
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index c99de4a21458..43d106598e82 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -20,6 +20,10 @@  config DMA_OPS
+# Lets platform IOMMU driver choose between bypass and IOMMU
+	bool