AT91: Fix power-saving in idle-mode on 926T processors

AT91: Fix power-saving in idle-mode on 926T processors

[Anders Larsen]

According to Atmel, their 926T processors (AT91 post RM9200) requires
'Wait for Interrupt' mode be entered right after disabling the processor clock
in order to minimise current consumption when idle, so do both provided we're
not running on a 920T (an RM9200).

Furthermore, get rid of the #ifndef CONFIG_DEBUG_KERNEL, since arch_idle()
can be turned off completely with the kernel parameter 'nohlt'.

Signed-off-by: Anders Larsen <al@alarsen.net>
Cc: Andrew Victor <avictor.za@gmail.com>
---
KernelVersion: 2.6.35

 arch/arm/mach-at91/include/mach/system.h |    7 +++----
 1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mach-at91/include/mach/system.h b/arch/arm/mach-at91/include/mach/system.h
index c80e090..ee8db15 100644
--- a/arch/arm/mach-at91/include/mach/system.h
+++ b/arch/arm/mach-at91/include/mach/system.h
@@ -28,17 +28,16 @@
 
 static inline void arch_idle(void)
 {
-#ifndef CONFIG_DEBUG_KERNEL
 	/*
 	 * Disable the processor clock.  The processor will be automatically
 	 * re-enabled by an interrupt or by a reset.
 	 */
 	at91_sys_write(AT91_PMC_SCDR, AT91_PMC_PCK);
-#else
+#ifndef CONFIG_CPU_ARM920T
 	/*
 	 * Set the processor (CP15) into 'Wait for Interrupt' mode.
-	 * Unlike disabling the processor clock via the PMC (above)
-	 *  this allows the processor to be woken via JTAG.
+	 * Post-RM9200 processors need this in conjunction with the above
+	 * to save power when idle.
 	 */
 	cpu_do_idle();
 #endif
-- 
1.7.0.4

Re: AT91: Fix power-saving in idle-mode on 926T processors

[Jean-Christophe PLAGNIOL-VILLARD]

On 21:44 Thu 07 Oct     , Anders Larsen wrote:
> According to Atmel, their 926T processors (AT91 post RM9200) requires
> 'Wait for Interrupt' mode be entered right after disabling the processor clock
> in order to minimise current consumption when idle, so do both provided we're
> not running on a 920T (an RM9200).
> 
> Furthermore, get rid of the #ifndef CONFIG_DEBUG_KERNEL, since arch_idle()
> can be turned off completely with the kernel parameter 'nohlt'.
> 
> Signed-off-by: Anders Larsen <al@alarsen.net>
> Cc: Andrew Victor <avictor.za@gmail.com>
please rebase against this branch

git://github.com/at91linux/linux-2.6-at91.git branch for-rmk

Best Regards,
J.

Re: AT91: Fix power-saving in idle-mode on 926T processors

[Nicolas Ferre]

Russell,

Le 08/10/2010 14:29, Jean-Christophe PLAGNIOL-VILLARD :
> On 21:44 Thu 07 Oct     , Anders Larsen wrote:
>> According to Atmel, their 926T processors (AT91 post RM9200) requires
>> 'Wait for Interrupt' mode be entered right after disabling the processor clock
>> in order to minimise current consumption when idle, so do both provided we're
>> not running on a 920T (an RM9200).
>>
>> Furthermore, get rid of the #ifndef CONFIG_DEBUG_KERNEL, since arch_idle()
>> can be turned off completely with the kernel parameter 'nohlt'.
>>
>> Signed-off-by: Anders Larsen <al@alarsen.net>
>> Cc: Andrew Victor <avictor.za@gmail.com>
> please rebase against this branch
> 
> git://github.com/at91linux/linux-2.6-at91.git branch for-rmk

This patch seems already in your "master" branch
(5c189208b606a85b4e97109af70d59f10a42fdfd).

Do you want me to rebase this patch or do you mange merging with "AT91:
fix use of clock disable on idle for AT91x40 devices"
(cb809b1a5ebffca8cf0314b788919989e8e4ab5f) ?
already in your "devel" and "devel-stable" branches?

Best regards,
-- 
Nicolas Ferre