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 \