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ARM: 6516/1: Allow SMP_ON_UP to work with Thumb-2 kernels.

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* __fixup_smp_on_up has been modified with support for the
    THUMB2_KERNEL case.  For THUMB2_KERNEL only, fixups are split
    into halfwords in case of misalignment, since we can't rely on
    unaligned accesses working before turning the MMU on.

    No attempt is made to optimise the aligned case, since the
    number of fixups is typically small, and it seems best to keep
    the code as simple as possible.

  * Add a rotate in the fixup_smp code in order to support
    CPU_BIG_ENDIAN, as suggested by Nicolas Pitre.

  * Add an assembly-time sanity-check to ALT_UP() to ensure that
    the content really is the right size (4 bytes).

    (No check is done for ALT_SMP().  Possibly, this could be fixed
    by splitting the two uses ot ALT_SMP() (ALT_SMP...SMP_UP versus
    ALT_SMP...SMP_UP_B) into two macros.  In the first case,
    ALT_SMP needs to expand to >= 4 bytes, not == 4.)

  * smp_mpidr.h (which implements ALT_SMP()/ALT_UP() manually due
    to macro limitations) has not been modified: the affected
    instruction (mov) has no 16-bit encoding, so the correct
    instruction size is satisfied in this case.

  * A "mode" parameter has been added to smp_dmb:

    smp_dmb arm @ assumes 4-byte instructions (for ARM code, e.g. kuser)
    smp_dmb     @ uses W() to ensure 4-byte instructions for ALT_SMP()

    This avoids assembly failures due to use of W() inside smp_dmb,
    when assembling pure-ARM code in the vectors page.

    There might be a better way to achieve this.

  * Kconfig: make SMP_ON_UP depend on
    (!THUMB2_KERNEL || !BIG_ENDIAN) i.e., THUMB2_KERNEL is now
    supported, but only if !BIG_ENDIAN (The fixup code for Thumb-2
    currently assumes little-endian order.)

Tested using a single generic realview kernel on:
	ARM RealView PB-A8 (CONFIG_THUMB2_KERNEL={n,y})
	ARM RealView PBX-A9 (SMP)

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Dave Martin 2010-12-01 15:39:23 +01:00 committed by Russell King
parent 86e62b9336
commit ed3768a8d9
4 changed files with 32 additions and 9 deletions
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2
arch/arm/Kconfig
View File

@ -1229,7 +1229,7 @@ config SMP
config SMP_ON_UP
bool "Allow booting SMP kernel on uniprocessor systems (EXPERIMENTAL)"
depends on EXPERIMENTAL
depends on SMP && !XIP && !THUMB2_KERNEL
depends on SMP && !XIP
default y
help
SMP kernels contain instructions which fail on non-SMP processors.

22
arch/arm/include/asm/assembler.h
View File

@ -157,16 +157,24 @@
#ifdef CONFIG_SMP
#define ALT_SMP(instr...) \
9998: instr
/*
* Note: if you get assembler errors from ALT_UP() when building with
* CONFIG_THUMB2_KERNEL, you almost certainly need to use
* ALT_SMP( W(instr) ... )
*/
#define ALT_UP(instr...) \
.pushsection ".alt.smp.init", "a" ;\
.long 9998b ;\
instr ;\
9997: instr ;\
.if . - 9997b != 4 ;\
.error "ALT_UP() content must assemble to exactly 4 bytes";\
.endif ;\
.popsection
#define ALT_UP_B(label) \
.equ up_b_offset, label - 9998b ;\
.pushsection ".alt.smp.init", "a" ;\
.long 9998b ;\
b . + up_b_offset ;\
W(b) . + up_b_offset ;\
.popsection
#else
#define ALT_SMP(instr...)
@ -177,16 +185,24 @@
/*
* SMP data memory barrier
*/
.macro smp_dmb
.macro smp_dmb mode
#ifdef CONFIG_SMP
#if __LINUX_ARM_ARCH__ >= 7
.ifeqs "\mode","arm"
ALT_SMP(dmb)
.else
ALT_SMP(W(dmb))
.endif
#elif __LINUX_ARM_ARCH__ == 6
ALT_SMP(mcr p15, 0, r0, c7, c10, 5) @ dmb
#else
#error Incompatible SMP platform
#endif
.ifeqs "\mode","arm"
ALT_UP(nop)
.else
ALT_UP(W(nop))
.endif
#endif
.endm

4
arch/arm/kernel/entry-armv.S
View File

@ -842,7 +842,7 @@ __kuser_helper_start:
*/
__kuser_memory_barrier: @ 0xffff0fa0
smp_dmb
smp_dmb arm
usr_ret lr
.align 5
@ -959,7 +959,7 @@ kuser_cmpxchg_fixup:
#else
smp_dmb
smp_dmb arm
1: ldrex r3, [r2]
subs r3, r3, r0
strexeq r3, r1, [r2]

13
arch/arm/kernel/head.S
View File

@ -412,10 +412,17 @@ __fixup_smp_on_up:
add r4, r4, r3
add r5, r5, r3
2: cmp r4, r5
movhs pc, lr
ldmia r4!, {r0, r6}
strlo r6, [r0, r3]
blo 2b
mov pc, lr
ARM( str r6, [r0, r3] )
THUMB( add r0, r0, r3 )
#ifdef __ARMEB__
THUMB( mov r6, r6, ror #16 ) @ Convert word order for big-endian.
#endif
THUMB( strh r6, [r0], #2 ) @ For Thumb-2, store as two halfwords
THUMB( mov r6, r6, lsr #16 ) @ to be robust against misaligned r3.
THUMB( strh r6, [r0] )
b 2b
ENDPROC(__fixup_smp)
1: .word .