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@xxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
Cc: Tony Lindgren <tony@xxxxxxxxxxx>
---
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(-)
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; \
})
--
1.8.3.2
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