This is a note to let you know that I've just added the patch titled
powerpc/4xx: Fix build errors from mfdcr()
to the 5.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-4xx-fix-build-errors-from-mfdcr.patch
and it can be found in the queue-5.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit b27d21974700740fd4c07a1225f3e6ccd9c03b91
Author: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Date: Thu Feb 18 23:30:58 2021 +1100
powerpc/4xx: Fix build errors from mfdcr()
[ Upstream commit eead089311f4d935ab5d1d8fbb0c42ad44699ada ]
lkp reported a build error in fsp2.o:
CC arch/powerpc/platforms/44x/fsp2.o
{standard input}:577: Error: unsupported relocation against base
Which comes from:
pr_err("GESR0: 0x%08x\n", mfdcr(base + PLB4OPB_GESR0));
Where our mfdcr() macro is stringifying "base + PLB4OPB_GESR0", and
passing that to the assembler, which obviously doesn't work.
The mfdcr() macro already checks that the argument is constant using
__builtin_constant_p(), and if not calls the out-of-line version of
mfdcr(). But in this case GCC is smart enough to notice that "base +
PLB4OPB_GESR0" will be constant, even though it's not something we can
immediately stringify into a register number.
Segher pointed out that passing the register number to the inline asm
as a constant would be better, and in fact it fixes the build error,
presumably because it gives GCC a chance to resolve the value.
While we're at it, change mtdcr() similarly.
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Suggested-by: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Acked-by: Feng Tang <feng.tang@xxxxxxxxx>
Link: https://lore.kernel.org/r/20210218123058.748882-1-mpe@xxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/include/asm/dcr-native.h b/arch/powerpc/include/asm/dcr-native.h
index 7141ccea8c94..a92059964579 100644
--- a/arch/powerpc/include/asm/dcr-native.h
+++ b/arch/powerpc/include/asm/dcr-native.h
@@ -53,8 +53,8 @@ static inline void mtdcrx(unsigned int reg, unsigned int val)
#define mfdcr(rn) \
({unsigned int rval; \
if (__builtin_constant_p(rn) && rn < 1024) \
- asm volatile("mfdcr %0," __stringify(rn) \
- : "=r" (rval)); \
+ asm volatile("mfdcr %0, %1" : "=r" (rval) \
+ : "n" (rn)); \
else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR))) \
rval = mfdcrx(rn); \
else \
@@ -64,8 +64,8 @@ static inline void mtdcrx(unsigned int reg, unsigned int val)
#define mtdcr(rn, v) \
do { \
if (__builtin_constant_p(rn) && rn < 1024) \
- asm volatile("mtdcr " __stringify(rn) ",%0" \
- : : "r" (v)); \
+ asm volatile("mtdcr %0, %1" \
+ : : "n" (rn), "r" (v)); \
else if (likely(cpu_has_feature(CPU_FTR_INDEXED_DCR))) \
mtdcrx(rn, v); \
else \
