powerpc: Add cpu_relax
Add a cpu_relax variant that uses SMT priority nop instructions like
Linux. This was split out of the SMP patch because it affects the sprs
test case.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-ID: <20240504122841.1177683-18-npiggin@gmail.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
diff --git a/lib/ppc64/asm/barrier.h b/lib/ppc64/asm/barrier.h
index d2df295..475434b 100644
--- a/lib/ppc64/asm/barrier.h
+++ b/lib/ppc64/asm/barrier.h
@@ -1,6 +1,7 @@
#ifndef _ASMPPC64_BARRIER_H_
#define _ASMPPC64_BARRIER_H_
+#define cpu_relax() asm volatile("or 1,1,1 ; or 2,2,2" ::: "memory")
#define pause_short() asm volatile(".long 0x7c40003c" ::: "memory")
#define mb() asm volatile("sync":::"memory")
diff --git a/powerpc/sprs.c b/powerpc/sprs.c
index 3387213..a85011a 100644
--- a/powerpc/sprs.c
+++ b/powerpc/sprs.c
@@ -228,8 +228,8 @@
[815] = { "TAR", 64, RW, },
[848] = { "IC", 64, HV_RW | OS_RO, SPR_ASYNC, },
[849] = { "VTB", 64, HV_RW | OS_RO, SPR_ASYNC, },
-[896] = { "PPR", 64, RW, },
-[898] = { "PPR32", 32, RW, },
+[896] = { "PPR", 64, RW, SPR_ASYNC, }, /* PPR(32) is changed by cpu_relax(), appears to be async */
+[898] = { "PPR32", 32, RW, SPR_ASYNC, },
[1023]= { "PIR", 32, OS_RO, SPR_ASYNC, }, /* Can't be virtualised, appears to be async */
};
