[PATCH 8/8] WIP: add a dma_alloc_contiguous API

[Christoph Hellwig]

Add a new API that returns a virtually non-contigous array of pages
and dma address.  This API is only implemented for dma-iommu and will
not be implemented for non-iommu DMA API instances that have to allocate
contiguous memory.  It is up to the caller to check if the API is
available.

The intent is that media drivers can use this API if either:

 - no kernel mapping or only temporary kernel mappings are required.
   That is as a better replacement for DMA_ATTR_NO_KERNEL_MAPPING
 - a kernel mapping is required for cached and DMA mapped pages, but
   the driver also needs the pages to e.g. map them to userspace.
   In that sense it is a replacement for some aspects of the recently
   removed and never fully implemented DMA_ATTR_NON_CONSISTENT

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
 drivers/iommu/dma-iommu.c   | 73 +++++++++++++++++++++++++------------
 include/linux/dma-mapping.h |  9 +++++
 kernel/dma/mapping.c        | 35 ++++++++++++++++++
 3 files changed, 93 insertions(+), 24 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 7922f545cd5eef..158026a856622c 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -565,23 +565,12 @@ static struct page **__iommu_dma_alloc_pages(struct device *dev,
 	return pages;
 }
 
-/**
- * iommu_dma_alloc_remap - Allocate and map a buffer contiguous in IOVA space
- * @dev: Device to allocate memory for. Must be a real device
- *	 attached to an iommu_dma_domain
- * @size: Size of buffer in bytes
- * @dma_handle: Out argument for allocated DMA handle
- * @gfp: Allocation flags
- * @prot: pgprot_t to use for the remapped mapping
- * @attrs: DMA attributes for this allocation
- *
- * If @size is less than PAGE_SIZE, then a full CPU page will be allocated,
+/*
+ * If size is less than PAGE_SIZE, then a full CPU page will be allocated,
  * but an IOMMU which supports smaller pages might not map the whole thing.
- *
- * Return: Mapped virtual address, or NULL on failure.
  */
-static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
-		dma_addr_t *dma_handle, gfp_t gfp, pgprot_t prot,
+static struct page **__iommu_dma_alloc_noncontiguous(struct device *dev,
+		size_t size, dma_addr_t *dma_handle, gfp_t gfp, pgprot_t prot,
 		unsigned long attrs)
 {
 	struct iommu_domain *domain = iommu_get_dma_domain(dev);
@@ -593,7 +582,6 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
 	struct page **pages;
 	struct sg_table sgt;
 	dma_addr_t iova;
-	void *vaddr;
 
 	*dma_handle = DMA_MAPPING_ERROR;
 
@@ -636,17 +624,10 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
 			< size)
 		goto out_free_sg;
 
-	vaddr = dma_common_pages_remap(pages, size, prot,
-			__builtin_return_address(0));
-	if (!vaddr)
-		goto out_unmap;
-
 	*dma_handle = iova;
 	sg_free_table(&sgt);
-	return vaddr;
+	return pages;
 
-out_unmap:
-	__iommu_dma_unmap(dev, iova, size);
 out_free_sg:
 	sg_free_table(&sgt);
 out_free_iova:
@@ -656,6 +637,46 @@ static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
 	return NULL;
 }
 
+static void *iommu_dma_alloc_remap(struct device *dev, size_t size,
+		dma_addr_t *dma_handle, gfp_t gfp, pgprot_t prot,
+		unsigned long attrs)
+{
+	struct page **pages;
+	void *vaddr;
+
+	pages = __iommu_dma_alloc_noncontiguous(dev, size, dma_handle, gfp,
+						prot, attrs);
+	if (!pages)
+		return NULL;
+	vaddr = dma_common_pages_remap(pages, size, prot,
+			__builtin_return_address(0));
+	if (!vaddr)
+		goto out_unmap;
+	return vaddr;
+
+out_unmap:
+	__iommu_dma_unmap(dev, *dma_handle, size);
+	__iommu_dma_free_pages(pages, PAGE_ALIGN(size) >> PAGE_SHIFT);
+	return NULL;
+}
+
+#ifdef CONFIG_DMA_REMAP
+static struct page **iommu_dma_alloc_noncontiguous(struct device *dev,
+		size_t size, dma_addr_t *dma_handle, gfp_t gfp,
+		unsigned long attrs)
+{
+	return __iommu_dma_alloc_noncontiguous(dev, size, dma_handle, gfp,
+					       PAGE_KERNEL, attrs);
+}
+
+static void iommu_dma_free_noncontiguous(struct device *dev, size_t size,
+		struct page **pages, dma_addr_t dma_handle)
+{
+	__iommu_dma_unmap(dev, dma_handle, size);
+	__iommu_dma_free_pages(pages, PAGE_ALIGN(size) >> PAGE_SHIFT);
+}
+#endif
+
 static void iommu_dma_sync_single_for_cpu(struct device *dev,
 		dma_addr_t dma_handle, size_t size, enum dma_data_direction dir)
 {
@@ -1110,6 +1131,10 @@ static const struct dma_map_ops iommu_dma_ops = {
 	.free			= iommu_dma_free,
 	.alloc_pages		= dma_common_alloc_pages,
 	.free_pages		= dma_common_free_pages,
+#ifdef CONFIG_DMA_REMAP
+	.alloc_noncontiguous	= iommu_dma_alloc_noncontiguous,
+	.free_noncontiguous	= iommu_dma_free_noncontiguous,
+#endif
 	.mmap			= iommu_dma_mmap,
 	.get_sgtable		= iommu_dma_get_sgtable,
 	.map_page		= iommu_dma_map_page,
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 4b9b1d64f5ec9e..51bbc32365bb8d 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -74,6 +74,10 @@ struct dma_map_ops {
 			gfp_t gfp);
 	void (*free_pages)(struct device *dev, size_t size, struct page *vaddr,
 			dma_addr_t dma_handle, enum dma_data_direction dir);
+	struct page **(*alloc_noncontiguous)(struct device *dev, size_t size,
+			dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs);
+	void (*free_noncontiguous)(struct device *dev, size_t size,
+			struct page **pages, dma_addr_t dma_handle);
 	int (*mmap)(struct device *, struct vm_area_struct *,
 			  void *, dma_addr_t, size_t,
 			  unsigned long attrs);
@@ -384,6 +388,11 @@ void *dma_alloc_noncoherent(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp);
 void dma_free_noncoherent(struct device *dev, size_t size, void *vaddr,
 		dma_addr_t dma_handle, enum dma_data_direction dir);
+bool dma_can_alloc_noncontiguous(struct device *dev);
+struct page **dma_alloc_noncontiguous(struct device *dev, size_t size,
+		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs);
+void dma_free_noncontiguous(struct device *dev, size_t size,
+		struct page **pages, dma_addr_t dma_handle);
 
 static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs)
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 06115f59f4ffbf..6d975d1a20dd72 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -529,6 +529,41 @@ void dma_free_noncoherent(struct device *dev, size_t size, void *vaddr,
 }
 EXPORT_SYMBOL_GPL(dma_free_noncoherent);
 
+bool dma_can_alloc_noncontiguous(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	return ops && ops->free_noncontiguous;
+}
+EXPORT_SYMBOL_GPL(dma_can_alloc_noncontiguous);
+
+struct page **dma_alloc_noncontiguous(struct device *dev, size_t size,
+		dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	if (WARN_ON_ONCE(!dma_can_alloc_noncontiguous(dev)))
+		return NULL;
+	if (attrs & ~DMA_ATTR_ALLOC_SINGLE_PAGES) {
+		dev_warn(dev, "invalid flags (0x%lx) for %s\n",
+			 attrs, __func__);
+		return NULL;
+	}
+	return ops->alloc_noncontiguous(dev, size, dma_handle, gfp, attrs);
+}
+EXPORT_SYMBOL_GPL(dma_alloc_noncontiguous);
+
+void dma_free_noncontiguous(struct device *dev, size_t size,
+		struct page **pages, dma_addr_t dma_handle)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	if (WARN_ON_ONCE(!dma_can_alloc_noncontiguous(dev)))
+		return;
+	ops->free_noncontiguous(dev, size, pages, dma_handle);
+}
+EXPORT_SYMBOL_GPL(dma_free_noncontiguous);
+
 int dma_supported(struct device *dev, u64 mask)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);
-- 
2.28.0