MIPS: Force o32 fp64 support on 32bit MIPS64r6 kernels

[ Upstream commit 2e6c7747 ]

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: 4e9d324d ("MIPS: Require O32 FP64 support for MIPS64 with O32 compat")
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 4.0.x-
Patchwork: https://patchwork.linux-mips.org/patch/15310/Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

arch/mips/Kconfig

@@ -1366,7 +1366,7 @@ 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