[PATCH 06/11] ARM: dma-mapping: Handle foreign buffers in arm_iommu_get_sgtable

[Mikko Perttunen]

arm_iommu_get_sgtable can only describe buffers which came from
arm_iommu_alloc_attrs, and returns -ENXIO for anything else. This is
stricter than iommu_dma_get_sgtable(), which falls back to describing
the buffer as a single chunk.

The difference shows up when a buffer is allocated for one device and
mapped for another, as TegraDRM does. Buffers are allocated on the
host1x logical device, which has no dma_configure and therefore uses
direct DMA ops, and are then mapped for a display controller behind the
SMMU.

Add the same fallback as iommu_dma_get_sgtable().

Signed-off-by: Mikko Perttunen <mperttunen@xxxxxxxxxx>
---
 arch/arm/mm/dma-mapping.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 91f12fb91509..22bde6acd1d3 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1169,12 +1169,29 @@ static int arm_iommu_get_sgtable(struct device *dev, struct sg_table *sgt,
 {
 	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
 	struct page **pages = __iommu_get_pages(cpu_addr, attrs);
+	struct page *page;
+	int ret;
 
-	if (!pages)
-		return -ENXIO;
+	if (pages)
+		return sg_alloc_table_from_pages(sgt, pages, count, 0, size,
+						 GFP_KERNEL);
 
-	return sg_alloc_table_from_pages(sgt, pages, count, 0, size,
-					 GFP_KERNEL);
+	/*
+	 * The buffer was not allocated through these DMA ops. It may belong to
+	 * a device which is not behind an IOMMU at all, which can happen when a
+	 * buffer is allocated on one device and mapped for another. Describe it
+	 * as a single chunk, as iommu_dma_get_sgtable() does.
+	 */
+	if (is_vmalloc_addr(cpu_addr))
+		page = vmalloc_to_page(cpu_addr);
+	else
+		page = virt_to_page(cpu_addr);
+
+	ret = sg_alloc_table(sgt, 1, GFP_KERNEL);
+	if (!ret)
+		sg_set_page(sgt->sgl, page, PAGE_ALIGN(size), 0);
+
+	return ret;
 }
 
 /*

-- 
2.55.0