[PATCH 16/20] tile PCI RC: add dma_get_required_mask()

From: Chris Metcalf
Date: Mon Aug 05 2013 - 16:43:19 EST

The standard kernel function dma_get_required_mask() uses the
highest DRAM address to determine if 32-bit or 64-bit DMA addressing
is needed. This only works on architectures that have direct mapping
between the PA and the PCI address space, i.e. those that don't have
I/O TLBs or have I/O TLB but choose to use direct mapping. Neither
of these are true for tilegx. Whether to use 64-bit DMA should depend
on the PCI device's capability only, not on the amount of DRAM
installeds, so we now advertise a 64-bit DMA mask unconditionally.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
arch/tile/include/asm/dma-mapping.h | 4 ++++
arch/tile/kernel/pci-dma.c | 18 ++++++++++++++++++
2 files changed, 22 insertions(+)

diff --git a/arch/tile/include/asm/dma-mapping.h b/arch/tile/include/asm/dma-mapping.h
index 6da0540..bd8387d 100644
--- a/arch/tile/include/asm/dma-mapping.h
+++ b/arch/tile/include/asm/dma-mapping.h
@@ -20,6 +20,10 @@
#include <linux/cache.h>
#include <linux/io.h>

+#ifdef __tilegx__
extern struct dma_map_ops *tile_dma_map_ops;
extern struct dma_map_ops *gx_pci_dma_map_ops;
extern struct dma_map_ops *gx_legacy_pci_dma_map_ops;
diff --git a/arch/tile/kernel/pci-dma.c b/arch/tile/kernel/pci-dma.c
index d16cfc1..3570ff7 100644
--- a/arch/tile/kernel/pci-dma.c
+++ b/arch/tile/kernel/pci-dma.c
@@ -590,3 +590,21 @@ int dma_set_coherent_mask(struct device *dev, u64 mask)
+ * The generic dma_get_required_mask() uses the highest physical address
+ * (max_pfn) to provide the hint to the PCI drivers regarding 32-bit or
+ * 64-bit DMA configuration. Since TILEGx has I/O TLB/MMU, allowing the
+ * DMAs to use the full 64-bit PCI address space and not limited by
+ * the physical memory space, we always let the PCI devices use
+ * 64-bit DMA if they have that capability, by returning the 64-bit
+ * DMA mask here. The device driver has the option to use 32-bit DMA if
+ * the device is not capable of 64-bit DMA.
+ */
+u64 dma_get_required_mask(struct device *dev)
+ return DMA_BIT_MASK(64);

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