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authorAndy Lutomirski <luto@amacapital.net>2013-05-13 23:58:40 +0000
committerDave Airlie <airlied@redhat.com>2013-05-31 13:02:52 +1000
commitd0d98eedee2178c803dd824bb09f52b0e2ac1811 (patch)
tree302ece15c574dc061b1dea4e67125c7b01342154 /include/linux/io.h
parente81f3d81e282a156b47c1c2c09a1976e34073060 (diff)
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Add arch_phys_wc_{add, del} to manipulate WC MTRRs if needed
Several drivers currently use mtrr_add through various #ifdef guards and/or drm wrappers. The vast majority of them want to add WC MTRRs on x86 systems and don't actually need the MTRR if PAT (i.e. ioremap_wc, etc) are working. arch_phys_wc_add and arch_phys_wc_del are new functions, available on all architectures and configurations, that add WC MTRRs on x86 if needed (and handle errors) and do nothing at all otherwise. They're also easier to use than mtrr_add and mtrr_del, so the call sites can be simplified. As an added benefit, this will avoid wasting MTRRs and possibly warning pointlessly on PAT-supporting systems. Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Dave Airlie <airlied@redhat.com>
Diffstat (limited to 'include/linux/io.h')
-rw-r--r--include/linux/io.h25
1 files changed, 25 insertions, 0 deletions
diff --git a/include/linux/io.h b/include/linux/io.h
index 069e407..f4f42fa 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 */
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