[PATCH RESEND] powerpc: add simd.h implementation specific to PowerPC

[Shawn Landden]

It is safe to do SIMD in an interrupt on PowerPC.
Only disable when there is no SIMD available
(and this is a static branch).

Tested and works with the WireGuard (Zinc) patch I wrote that needs this.
Also improves performance of the crypto subsystem that checks this.

Re-sending because this linuxppc-dev didn't seem to accept it.

Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=203571
Signed-off-by: Shawn Landden <shawn at git.icu>
---
 arch/powerpc/include/asm/simd.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 arch/powerpc/include/asm/simd.h

diff --git a/arch/powerpc/include/asm/simd.h b/arch/powerpc/include/asm/simd.h
new file mode 100644
index 000000000..b3fecb95a
--- /dev/null
+++ b/arch/powerpc/include/asm/simd.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+
+#include <asm/cpu_has_feature.h>
+
+/*
+ * may_use_simd - whether it is allowable at this time to issue SIMD
+ *                instructions or access the SIMD register file
+ *
+ * As documented in Chapter 6.2.1 Machine Status Save/Restore Registers
+ * of Power ISA (2.07 and 3.0), all registers are saved/restored in an interrupt.
+ */
+static inline bool may_use_simd(void)
+{
+	return !cpu_has_feature(CPU_FTR_FPU_UNAVAILABLE);
+}
-- 
2.21.0.1020.gf2820cf01a