diff options
Diffstat (limited to 'include/linux/io.h')
| -rw-r--r-- | include/linux/io.h | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/include/linux/io.h b/include/linux/io.h index 069e4075f872..f4f42faec686 100644 --- a/include/linux/io.h +++ b/include/linux/io.h @@ -76,4 +76,29 @@ void devm_ioremap_release(struct device *dev, void *res); #define arch_has_dev_port() (1) #endif +/* + * Some systems (x86 without PAT) have a somewhat reliable way to mark a + * physical address range such that uncached mappings will actually + * end up write-combining. This facility should be used in conjunction + * with pgprot_writecombine, ioremap-wc, or set_memory_wc, since it has + * no effect if the per-page mechanisms are functional. + * (On x86 without PAT, these functions manipulate MTRRs.) + * + * arch_phys_del_wc(0) or arch_phys_del_wc(any error code) is guaranteed + * to have no effect. + */ +#ifndef arch_phys_wc_add +static inline int __must_check arch_phys_wc_add(unsigned long base, + unsigned long size) +{ + return 0; /* It worked (i.e. did nothing). */ +} + +static inline void arch_phys_wc_del(int handle) +{ +} + +#define arch_phys_wc_add arch_phys_wc_add +#endif + #endif /* _LINUX_IO_H */ |