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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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