| Message ID | alpine.DEB.2.02.1307301125420.4505@utopia.booyaka.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Jul 30, 2013 at 12:32:06PM +0100, Paul Walmsley wrote: > > Commit 621a0147d5c921f4cc33636ccd0602ad5d7cbfbc ("ARM: 7757/1: mm: > don't flush icache in switch_mm with hardware broadcasting") breaks > the boot on OMAP2430SDP with omap2plus_defconfig. Tracked to an > undefined instruction abort from the CP15 read in > cache_ops_need_broadcast(). It turns out that gcc 4.5 reorders the > extended CP15 read above the is_smp() test. This breaks ARM1136 r0 > cores, since they don't support several CP15 registers that later ARM > cores do. ARM1136JF-S TRM section 3.2.1 "Register allocation" has the > details. > > So mark the extended CP15 read as clobbering memory, which prevents > the compiler from reordering it before the is_smp() test. Russell > states that the code generated from this approach is preferable to > marking the inline asm as volatile. Remove the existing condition > code clobber as it's obsolete, per Nico's post: > > http://www.spinics.net/lists/arm-kernel/msg261208.html > > This patch is a collaboration with Will Deacon and Russell King. > > Signed-off-by: Paul Walmsley <paul@pwsan.com> > Cc: Will Deacon <will.deacon@arm.com> > Cc: Russell King <rmk+kernel@arm.linux.org.uk> > Cc: Nicolas Pitre <nicolas.pitre@linaro.org> > Cc: Tony Lindgren <tony@atomide.com> > --- Acked-by: Will Deacon <will.deacon@arm.com> Will -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h index 8c25dc4..9672e97 100644 --- a/arch/arm/include/asm/cputype.h +++ b/arch/arm/include/asm/cputype.h @@ -89,13 +89,18 @@ extern unsigned int processor_id; __val; \ }) +/* + * The memory clobber prevents gcc 4.5 from reordering the mrc before + * any is_smp() tests, which can cause undefined instruction aborts on + * ARM1136 r0 due to the missing extended CP15 registers. + */ #define read_cpuid_ext(ext_reg) \ ({ \ unsigned int __val; \ asm("mrc p15, 0, %0, c0, " ext_reg \ : "=r" (__val) \ : \ - : "cc"); \ + : "memory"); \ __val; \ })
Commit 621a0147d5c921f4cc33636ccd0602ad5d7cbfbc ("ARM: 7757/1: mm: don't flush icache in switch_mm with hardware broadcasting") breaks the boot on OMAP2430SDP with omap2plus_defconfig. Tracked to an undefined instruction abort from the CP15 read in cache_ops_need_broadcast(). It turns out that gcc 4.5 reorders the extended CP15 read above the is_smp() test. This breaks ARM1136 r0 cores, since they don't support several CP15 registers that later ARM cores do. ARM1136JF-S TRM section 3.2.1 "Register allocation" has the details. So mark the extended CP15 read as clobbering memory, which prevents the compiler from reordering it before the is_smp() test. Russell states that the code generated from this approach is preferable to marking the inline asm as volatile. Remove the existing condition code clobber as it's obsolete, per Nico's post: http://www.spinics.net/lists/arm-kernel/msg261208.html This patch is a collaboration with Will Deacon and Russell King. Signed-off-by: Paul Walmsley <paul@pwsan.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Cc: Nicolas Pitre <nicolas.pitre@linaro.org> Cc: Tony Lindgren <tony@atomide.com> --- Intended for v3.11-rc. Basic test logs available here: http://www.pwsan.com/omap/testlogs/bisect_2430sdp_hang_v3.11-rc/20130730045715/ N.B., several boards have problems on v3.11-rc that are unrelated to this patch. arch/arm/include/asm/cputype.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)