Introduce a new dax_is_supported() static inline to check whether the
architecture supports DAX.

This replaces the following fs/Kconfig:FS_DAX dependency:

  depends on !(ARM || MIPS || SPARC)

This is done in preparation for its use by each filesystem supporting
the dax mount option to validate whether dax is indeed supported.

This is done in preparation for using dcache_is_aliasing() in a
following change which will properly support architectures which detect
dcache aliasing at runtime.

Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing 
caches")
Signed-off-by: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: Dan Williams <[email protected]>
Cc: Vishal Verma <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Russell King <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
 fs/Kconfig          |  1 -
 include/linux/dax.h | 10 ++++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index 42837617a55b..e5efdb3b276b 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -56,7 +56,6 @@ endif # BLOCK
 config FS_DAX
        bool "File system based Direct Access (DAX) support"
        depends on MMU
-       depends on !(ARM || MIPS || SPARC)
        depends on ZONE_DEVICE || FS_DAX_LIMITED
        select FS_IOMAP
        select DAX
diff --git a/include/linux/dax.h b/include/linux/dax.h
index b463502b16e1..cfc8cd4a3eae 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -78,6 +78,12 @@ static inline bool daxdev_mapping_supported(struct 
vm_area_struct *vma,
                return false;
        return dax_synchronous(dax_dev);
 }
+static inline bool dax_is_supported(void)
+{
+       return !IS_ENABLED(CONFIG_ARM) &&
+              !IS_ENABLED(CONFIG_MIPS) &&
+              !IS_ENABLED(CONFIG_SPARC);
+}
 #else
 static inline void *dax_holder(struct dax_device *dax_dev)
 {
@@ -122,6 +128,10 @@ static inline size_t dax_recovery_write(struct dax_device 
*dax_dev,
 {
        return 0;
 }
+static inline bool dax_is_supported(void)
+{
+       return false;
+}
 #endif
 
 void set_dax_nocache(struct dax_device *dax_dev);
-- 
2.39.2


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