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1ad77a876d
This patch provides an ARM implementation of ioremap_wc(). We use different page table attributes depending on which CPU we are running on: - Non-XScale ARMv5 and earlier systems: The ARMv5 ARM documents four possible mapping types (CB=00/01/10/11). We can't use any of the cached memory types (CB=10/11), since that breaks coherency with peripheral devices. Both CB=00 and CB=01 are suitable for _wc, and CB=01 (Uncached/Buffered) allows the hardware more freedom than CB=00, so we'll use that. (The ARMv5 ARM seems to suggest that CB=01 is allowed to delay stores but isn't allowed to merge them, but there is no other mapping type we can use that allows the hardware to delay and merge stores, so we'll go with CB=01.) - XScale v1/v2 (ARMv5): same as the ARMv5 case above, with the slight difference that on these platforms, CB=01 actually _does_ allow merging stores. (If you want noncoalescing bufferable behavior on Xscale v1/v2, you need to use XCB=101.) - Xscale v3 (ARMv5) and ARMv6+: on these systems, we use TEXCB=00100 mappings (Inner/Outer Uncacheable in xsc3 parlance, Uncached Normal in ARMv6 parlance). The ARMv6 ARM explicitly says that any accesses to Normal memory can be merged, which makes Normal memory more suitable for _wc mappings than Device or Strongly Ordered memory, as the latter two mapping types are guaranteed to maintain transaction number, size and order. We use the Uncached variety of Normal mappings for the same reason that we can't use C=1 mappings on ARMv5. The xsc3 Architecture Specification documents TEXCB=00100 as being Uncacheable and allowing coalescing of writes, which is also just what we need. Signed-off-by: Lennert Buytenhek <buytenh@marvell.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> |
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| .gitignore | ||
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