[at91] Save power by disabling the processor clock when CPU is idle

[at91] Save power by disabling the processor clock when CPU is idle

[Anders Larsen]

Disable the processor clock when the CPU is idle.

This saves much more power than merely entering 'Wait for Interrupt' mode.
Since JTAG-debugging doesn't work when the processor clock is switched off,
make it conditional on CONFIG_DEBUG_KERNEL.

Signed-off-by: Anders Larsen <al@alarsen.net>
Cc: Andrew Victor <avictor.za@gmail.com>
---
KernelVersion: 2.6.33

 arch/arm/mach-at91/include/mach/system.h |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)


Index: b/arch/arm/mach-at91/include/mach/system.h
===================================================================
--- a/arch/arm/mach-at91/include/mach/system.h
+++ b/arch/arm/mach-at91/include/mach/system.h
@@ -24,21 +24,24 @@
 #include <mach/hardware.h>
 #include <mach/at91_st.h>
 #include <mach/at91_dbgu.h>
+#include <mach/at91_pmc.h>
 
 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);
-
+	at91_sys_write(AT91_PMC_SCDR, AT91_PMC_PCK);
+#else
 	/*
 	 * 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.
 	 */
 	cpu_do_idle();
+#endif
 }
 
 void (*at91_arch_reset)(void);

[at91] Save power by disabling the processor clock when CPU is idle

[avictor.za at gmail.com]

> Disable the processor clock when the CPU is idle.
>
> This saves much more power than merely entering 'Wait for Interrupt' mode.
> Since JTAG-debugging doesn't work when the processor clock is switched off,
> make it conditional on CONFIG_DEBUG_KERNEL.
>
> Signed-off-by: Anders Larsen <al@alarsen.net>
> Cc: Andrew Victor <avictor.za@gmail.com>

Acked-by: Andrew Victor <linux@maxim.org.za>

Russell:  It is patch 6053/1 in the patch-system.

[at91] Save power by disabling the processor clock when CPU is idle

[Russell King - ARM Linux]

On Sun, May 02, 2010 at 10:10:29PM +0200, avictor.za at gmail.com wrote:
> > Disable the processor clock when the CPU is idle.
> >
> > This saves much more power than merely entering 'Wait for Interrupt' mode.
> > Since JTAG-debugging doesn't work when the processor clock is switched off,
> > make it conditional on CONFIG_DEBUG_KERNEL.
> >
> > Signed-off-by: Anders Larsen <al@alarsen.net>
> > Cc: Andrew Victor <avictor.za@gmail.com>
> 
> Acked-by: Andrew Victor <linux@maxim.org.za>
> 
> Russell:  It is patch 6053/1 in the patch-system.

Ok, thanks.  Where do we stand wrt the other two patches (5966/1 and
5967/1) ?

[at91] Save power by disabling the processor clock when CPU is idle

[avictor.za at gmail.com]

hi Russell,

> Ok, thanks. ?Where do we stand wrt the other two patches (5966/1 and
> 5967/1) ?

They can be applied.  Thanks.

Acked-by: Andrew Victor <linux@maxim.org.za>

[at91] Save power by disabling the processor clock when CPU is idle

[Uwe Kleine-König]

Hello,

On Tue, Apr 13, 2010 at 01:05:32PM +0200, Anders Larsen wrote:
> Disable the processor clock when the CPU is idle.
> 
> This saves much more power than merely entering 'Wait for Interrupt' mode.
> Since JTAG-debugging doesn't work when the processor clock is switched off,
> make it conditional on CONFIG_DEBUG_KERNEL.
> 
> Signed-off-by: Anders Larsen <al@alarsen.net>
> Cc: Andrew Victor <avictor.za@gmail.com>
> ---
> KernelVersion: 2.6.33
> 
>  arch/arm/mach-at91/include/mach/system.h |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> 
> Index: b/arch/arm/mach-at91/include/mach/system.h
> ===================================================================
> --- a/arch/arm/mach-at91/include/mach/system.h
> +++ b/arch/arm/mach-at91/include/mach/system.h
> @@ -24,21 +24,24 @@
>  #include <mach/hardware.h>
>  #include <mach/at91_st.h>
>  #include <mach/at91_dbgu.h>
> +#include <mach/at91_pmc.h>
>  
>  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);
> -
> +	at91_sys_write(AT91_PMC_SCDR, AT91_PMC_PCK);
> +#else
>  	/*
>  	 * 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.
>  	 */
>  	cpu_do_idle();
> +#endif

There is a kernel parameter (IIRC "nohlt") that should take care of
this?!

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

[at91] Save power by disabling the processor clock when CPU is idle

[Anders Larsen]

Hello,

On 2010-05-05 22:25:29, Uwe Kleine-K?nig wrote:
> There is a kernel parameter (IIRC "nohlt") that should take care of
> this?!

I hadn't noticed that one (it's operating several layers above the piece
of code I modified).

So it seems we could do way with the #else clause completely (requiring
the user to set 'nohlt' when debugging with JTAG)?

Cheers
Anders
-- 
happy 'ptxdist' user