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| author | Chris Metcalf <cmetcalf@tilera.com> | 2013-08-12 15:25:22 -0400 |
|---|---|---|
| committer | Chris Metcalf <cmetcalf@tilera.com> | 2013-09-03 14:52:20 -0400 |
| commit | 5e7705df28720c424c11bdedf0d568177351c55a (patch) | |
| tree | 28c341353900c87e7ddcd097bb8e599070b3bbf7 | |
| parent | bdb8205455a31362fc72075583aedd63ff0c944b (diff) | |
| download | linux-5e7705df28720c424c11bdedf0d568177351c55a.tar.bz2 | |
tile PCI RC: add comment about "PCI hole" problem
Explain the rationale of not overlapping the 64-bit DMA window
with the PA range.
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
| -rw-r--r-- | arch/tile/include/asm/pci.h | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/tile/include/asm/pci.h b/arch/tile/include/asm/pci.h index c99ad44233f4..dfedd7ac7298 100644 --- a/arch/tile/include/asm/pci.h +++ b/arch/tile/include/asm/pci.h @@ -122,6 +122,11 @@ static inline void pci_iounmap(struct pci_dev *dev, void __iomem *addr) {} * the CPA plus TILE_PCI_MEM_MAP_BASE_OFFSET. To support 32-bit * devices, we create a separate map region that handles the low * 4GB. + * + * This design lets us avoid the "PCI hole" problem where the host bridge + * won't pass DMA traffic with target addresses that happen to fall within the + * BAR space. This enables us to use all the physical memory for DMA, instead + * of wasting the same amount of physical memory as the BAR window size. */ #define TILE_PCI_MEM_MAP_BASE_OFFSET (1ULL << CHIP_PA_WIDTH()) |