[linux-pm] [RFC PATCH v4] ARM hibernation/suspend-to-disk support

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Thu, Jun 09, 2011 at 06:12:55PM +0100, Russell King - ARM Linux wrote:
> > 3. Avoid direct write to AUXCTRL in generic suspend code.
> 
> This is the only problematical one that I can see.  We need to restore
> this on systems running in secure mode.  What we could do is rather than
> writing to the register, read it first and compare its value with what
> was saved to see whether we need to write it.
> 
> Then, if platforms run in non-secure mode, they are responsible for
> restoring that register back to its pre-suspend value before their
> assembly calls cpu_resume().

And here's a patch which does that:

8<-----------
From: Russell King <rmk+kernel@arm.linux.org.uk>
ARM: Avoid writing to auxctrl register unless it needs to be updated

As the auxiliary control register is not writable in non-secure mode
such as on OMAP, we must avoid writing the register when resuming in
non-secure mode.  Avoid this by moving the responsibility to the
SoC code in this case to ensure that the auxiliary control register
is restored before cpu_resume() is called.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
--
 arch/arm/mm/proc-v7.S |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 3c38678..fa1e6d5 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -237,7 +237,9 @@ ENTRY(cpu_v7_do_resume)
 	mcr	p15, 0, r7, c2, c0, 0	@ TTB 0
 	mcr	p15, 0, r8, c2, c0, 1	@ TTB 1
 	mcr	p15, 0, ip, c2, c0, 2	@ TTB control register
-	mcr	p15, 0, r10, c1, c0, 1	@ Auxiliary control register
+	mrc	p15, 0, r4, c1, c0, 1	@ Read auxiliary control register
+	teq	r4, r10
+	mcrne	p15, 0, r10, c1, c0, 1	@ Auxiliary control register
 	mcr	p15, 0, r11, c1, c0, 2	@ Co-processor access control
 	ldr	r4, =PRRR		@ PRRR
 	ldr	r5, =NMRR		@ NMRR