linux-kernel - Re: [PATCH] ARM: Fix SMP_ON_UP for non ARM ltd. implementations

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Message-ID: <20110130164007.GA27436@n2100.arm.linux.org.uk>
Date:	Sun, 30 Jan 2011 16:40:07 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Will Deacon <will.deacon@....com>
Cc:	Stephen Boyd <sboyd@...eaurora.org>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: Fix SMP_ON_UP for non ARM ltd. implementations

On Sun, Jan 30, 2011 at 04:27:55PM +0000, Will Deacon wrote:
> >         mrc     p15, 0, r0, c0, c0, 5   @ read MPIDR
> 
> 
> The code following this does:
> 
> tst     r0, #1 << 31
> movne   pc, lr                  @ bit 31 => SMP
> 
> As an optimisation, we could also check that bit 30 is zero so that
> we patch out the SMP stuff for single-core A5/A9/A15. Up to you.

Ok, so with that added, it becomes:

 arch/arm/kernel/head.S |   22 ++++++++++------------
 1 files changed, 10 insertions(+), 12 deletions(-)

diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index f17d9a0..c0225da 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -392,24 +392,22 @@ ENDPROC(__turn_mmu_on)
 
 #ifdef CONFIG_SMP_ON_UP
 __fixup_smp:
-	mov	r4, #0x00070000
-	orr	r3, r4, #0xff000000	@ mask 0xff070000
-	orr	r4, r4, #0x41000000	@ val 0x41070000
-	and	r0, r9, r3
-	teq	r0, r4			@ ARM CPU and ARMv6/v7?
+	and	r3, r9, #0x000f0000	@ architecture version
+	teq	r3, #0x000f0000		@ CPU ID supported?
 	bne	__fixup_smp_on_up	@ no, assume UP
 
-	orr	r3, r3, #0x0000ff00
-	orr	r3, r3, #0x000000f0	@ mask 0xff07fff0
+	bic	r3, r9, #0x00ff0000
+	bic	r3, r3, #0x0000000f	@ mask 0xff00fff0
+	mov	r4, #0x41000000
 	orr	r4, r4, #0x0000b000
-	orr	r4, r4, #0x00000020	@ val 0x4107b020
-	and	r0, r9, r3
-	teq	r0, r4			@ ARM 11MPCore?
+	orr	r4, r4, #0x00000020	@ val 0x4100b020
+	teq	r3, r4			@ ARM 11MPCore?
 	moveq	pc, lr			@ yes, assume SMP
 
 	mrc	p15, 0, r0, c0, c0, 5	@ read MPIDR
-	tst	r0, #1 << 31
-	movne	pc, lr			@ bit 31 => SMP
+	and	r0, r0, #0xc0000000	@ multiprocessing extensions and
+	teq	r0, #0x80000000		@ not part of a uniprocessor system?
+	moveq	pc, lr			@ yes, assume SMP
 
 __fixup_smp_on_up:
 	adr	r0, 1f
--
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