[PATCH] OMAP3: remove useless ASA bit from AUXCR

[Siarhei Siamashka]

Setting ASA bit hurts performance for the code which has lots of I-cache
misses and there are no Cortex-A8 errata workarounds which would require
to have it.

A test program which intentionally stresses I-cache misses on conditional
branches is attached.

ASA bit is not set:

real    0m2.940s
user    0m2.930s
sys     0m0.008s

ASA bit is set:

real    0m3.470s
user    0m3.461s
sys     0m0.008s

The difference on some real applications is much more modest and is just
something like ~0.5%, but every little bit helps.

/**** start of bench_ASA.c ****/
void __attribute__((naked)) f(int count, void *rand)
{
    asm volatile (
        "    push   {r4, r5, r6, lr}\n"
        "    mov    r4, r0\n"
        "    mov    r5, r1\n"
        "0:\n"
        ".rept 4096\n"
        "    blx    r5\n"
        "    tst    r0, #1\n"
        "    bne    1f\n"
        "    b      2f\n"
        ".balign 64\n"
        "1:\n"
        ".rept 15\n"
        "    add    r0, r0, #0\n"
        ".endr\n"
        "    b      3f\n"
        ".balign 64\n"
        "2:\n"
        ".rept 16\n"
        "    add    r0, r0, #0\n"
        ".endr\n"
        "3:\n"
        ".endr\n"
        "    subs r4, r4, #1\n"
        "    bgt  0b\n"
        "    pop  {r4, r5, r6, pc}\n"
    );
}
int main()
{
    f(1000, rand);
    return 0;
}
/**** end of bench_ASA.c ****/

Signed-off-by: Siarhei Siamashka <siarhei.siamashka at gmail.com>
---
 arch/arm/cpu/armv7/omap3/cache.S |    1 -
 1 files changed, 0 insertions(+), 1 deletions(-)

diff --git a/arch/arm/cpu/armv7/omap3/cache.S b/arch/arm/cpu/armv7/omap3/cache.S
index cda87ba..2854771 100644
--- a/arch/arm/cpu/armv7/omap3/cache.S
+++ b/arch/arm/cpu/armv7/omap3/cache.S
@@ -169,7 +169,6 @@ setup_auxcr:
 	orr	r1, r3, r2, lsr #20-4		@ combine variant and revision
 	mov	r12, #0x3
 	mrc	p15, 0, r0, c1, c0, 1
-	orr	r0, r0, #0x10			@ Enable ASA
 	@ Enable L1NEON on pre-r2p1 (erratum 621766 workaround)
 	cmp	r1, #0x21
 	orrlt	r0, r0, #1 << 5
-- 
1.7.3.2


Best regards,

Wolfgang Denk

-- 
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