On Wed, Feb 01, 2017 at 01:44:02PM +0000, Robin Murphy wrote:

Hi Nate,

On 31/01/17 20:16, Nate Watterson wrote:

quoted

Some drivers set the dma_mask of client devices based solely on values
read from capability registers which may not account for platform
specific bus address width limitations. Fortunately, the ACPI IORT table
provides a way to report the effective number of address bits a device
can use to access memory. This information, when present, is used to
supplement the checks already being done in dma_supported() to avoid
setting overly generous dma_masks.

This is equally a problem for DT, and I think in general we'd prefer not
to be dragging ACPI/DT specifics in at this level when there's a clean
way to address it more generally. There is some recent ongoing
discussion and work in this area (latest part at [1]) - I have a local
branch somewhere implementing the stricter "don't special case default
masks" version (after I came around to Arnd's viewpoint), which I must
refresh myself on because there was some anomaly in the core DT code
which that brought to light.

Agreed. I can prototype the ACPI version by using the _DMA object in the
ACPI specs instead of IORT specific bindings (what to do for named
components has to be seen given that _DMA object and IORT bindings can
provide different information - though _DMA object usage at least on x86
seems non-existent, whether we should use it or not on ARM is still a
question mark). Anyway, the IORT parsing code in patch 1 is simple, we
have to decide how to handle the information retrieved. I will have a
look at [1] let me know if you need help prototyping and testing it with
ACPI.

Lorenzo

quoted

Signed-off-by: Nate Watterson <redacted>
---
 arch/arm64/mm/dma-mapping.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index e040827..467fd23 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c

@@ -19,6 +19,7 @@
 
 #include <linux/gfp.h>
 #include <linux/acpi.h>
+#include <linux/acpi_iort.h>
 #include <linux/bootmem.h>
 #include <linux/cache.h>
 #include <linux/export.h>

@@ -347,6 +348,12 @@ static int __swiotlb_get_sgtable(struct device *dev, struct sg_table *sgt,
 
 static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
 {
+	int dma_limit;
+
+	dma_limit = iort_get_memory_address_limit(hwdev);
+	if (dma_limit >= 0 && DMA_BIT_MASK(dma_limit) < mask)
+		return 0;
+
 	if (swiotlb)
 		return swiotlb_dma_supported(hwdev, mask);
 	return 1;

@@ -784,6 +791,17 @@ static void __iommu_unmap_sg_attrs(struct device *dev,
 	iommu_dma_unmap_sg(dev, sgl, nelems, dir, attrs);
 }
 
+static int __iommu_dma_supported(struct device *hwdev, u64 mask)
+{
+	int dma_limit;
+
+	dma_limit = iort_get_memory_address_limit(hwdev);
+	if (dma_limit >= 0 && DMA_BIT_MASK(dma_limit) < mask)
+		return 0;
+
+	return iommu_dma_supported(hwdev, mask);

Either way, this reminds me that iommu_dma_supported() is another thing
I got completely wrong - time to write yet another patch...

Robin.

[1]:http://www.mail-archive.com/linux-renesas-soc at vger.kernel.org/msg10637.html

quoted

+}
+
 static struct dma_map_ops iommu_dma_ops = {
 	.alloc = __iommu_alloc_attrs,
 	.free = __iommu_free_attrs,

@@ -799,7 +817,7 @@ static void __iommu_unmap_sg_attrs(struct device *dev,
 	.sync_sg_for_device = __iommu_sync_sg_for_device,
 	.map_resource = iommu_dma_map_resource,
 	.unmap_resource = iommu_dma_unmap_resource,
-	.dma_supported = iommu_dma_supported,
+	.dma_supported = __iommu_dma_supported,
 	.mapping_error = iommu_dma_mapping_error,
 };