[PATCH 4.4 27/32] MIPS: Force o32 fp64 support on 32bit MIPS64r6 kernels

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: James Hogan <james.hogan@xxxxxxxxxx>

commit 2e6c7747730296a6d4fd700894286db1132598c4 upstream.

When a 32-bit kernel is configured to support MIPS64r6 (CPU_MIPS64_R6),
MIPS_O32_FP64_SUPPORT won't be selected as it should be because
MIPS32_O32 is disabled (o32 is already the default ABI available on
32-bit kernels).

This results in userland FP breakage as CP0_Status.FR is read-only 1
since r6 (when an FPU is present) so __enable_fpu() will fail to clear
FR. This causes the FPU emulator to get used which will incorrectly
emulate 32-bit FPU registers.

Force o32 fp64 support in this case by also selecting
MIPS_O32_FP64_SUPPORT from CPU_MIPS64_R6 if 32BIT.

Fixes: 4e9d324d4288 ("MIPS: Require O32 FP64 support for MIPS64 with O32 compat")
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Reviewed-by: Paul Burton <paul.burton@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/15310/
Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/mips/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1412,7 +1412,7 @@ config CPU_MIPS32_R6
 	select CPU_SUPPORTS_MSA
 	select GENERIC_CSUM
 	select HAVE_KVM
-	select MIPS_O32_FP64_SUPPORT
+	select MIPS_O32_FP64_SUPPORT if 32BIT
 	help
 	  Choose this option to build a kernel for release 6 or later of the
 	  MIPS32 architecture.  New MIPS processors, starting with the Warrior