[SPARC]: Mark as emulating cmpxchg, add appropriate depends for DRM.

The DRM code depends on an atomic version of cmpxchg(), which is not
available on sparc32. Since other platforms besides sparc32 have this
issue a KCONFIG option is added for it.

Signed-off-by: Martin Habets <errandir_news@mph.eclipse.co.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 8 insertions, 1 deletions

diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index bd992c0048f0..fbcc00c6c06e 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -178,6 +178,13 @@ config ARCH_HAS_ILOG2_U64
         bool
         default n
 
+config EMULATED_CMPXCHG
+        bool
+        default y
+        help
+          Sparc32 does not have a CAS instruction like sparc64. cmpxchg()
+          is emulated, and therefore it is not completely atomic.
+
 config SUN_PM
         bool
         default y
diff --git a/drivers/char/drm/Kconfig b/drivers/char/drm/Kconfig
index ef833a1c27eb..0b7ffa5191c6 100644
--- a/drivers/char/drm/Kconfig
+++ b/drivers/char/drm/Kconfig
@@ -6,7 +6,7 @@
 #
 config DRM
         tristate "Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)"
-        depends on (AGP || AGP=n) && PCI
+        depends on (AGP || AGP=n) && PCI && !EMULATED_CMPXCHG
         help
           Kernel-level support for the Direct Rendering Infrastructure (DRI)
           introduced in XFree86 4.0. If you say Y here, you need to select