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SubjectRe: [at91] Save power by disabling the processor clock when CPU is idle
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-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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