[PATCH v2 04/22] PCI: fix pci_remap_iospace() remap attribute

Lorenzo Pieralisi
2017-03-27T09:51:06Z

According to the PCI local bus specifications (Revision 3.0, 3.2.5),
I/O Address space transactions are non-posted. On architectures where
I/O space is implemented through a chunk of memory mapped space mapped
to PCI address space (ie IA64/ARM/ARM64) the memory mapping for the
region backing I/O Address Space transactions determines the I/O
transactions attributes (before the transactions actually reaches the
PCI bus where it is handled according to the PCI specifications).

Current pci_remap_iospace() interface, that is used to map the PCI I/O
Address Space into virtual address space, use pgprot_device() as memory
attribute for the virtual address mapping, that in some architectures
(ie ARM64) provides non-cacheable but write bufferable mappings (ie
posted writes), which clash with the non-posted write behaviour for I/O
Address Space mandated by the PCI specifications.

Update the prot ioremap_page_range() parameter in pci_remap_iospace()
to pgprot_nonposted to ensure that the virtual mapping backing
I/O Address Space guarantee non-posted write transactions issued
when addressing I/O Address Space through the MMIO mapping.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
---
drivers/pci/pci.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index bd98674..9e084c0 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3375,7 +3375,7 @@ int pci_remap_iospace(const struct resource *res, phys_addr_t phys_addr)
return -EINVAL;

return ioremap_page_range(vaddr, vaddr + resource_size(res), phys_addr,
- pgprot_device(PAGE_KERNEL));
+ pgprot_nonposted(PAGE_KERNEL));
#else
/* this architecture does not have memory mapped I/O space,
so this function should never be called */
--
2.10.0