On Tue, May 8, 2012 at 3:47 PM, AnilKumar, Chimata <anilkumar@xxxxxx> wrote:
> On Mon, May 07, 2012 at 10:51:53, J, KEERTHY wrote:
>> On Fri, May 4, 2012 at 2:42 PM, AnilKumar, Chimata <anilkumar@xxxxxx> wrote:
>> > On Thu, Apr 26, 2012 at 23:10:36, J, KEERTHY wrote:
>> >> From: Jean Pihet <j-pihet@xxxxxx>
>> >>
>> >> Now that omap_test_timeout is only accessible from mach-omap2/,
>> >> introduce a similar function for SR.
>> >>
>> >> This change makes the SmartReflex implementation ready for the move
>> >> to drivers/.
>> >>
>> >> Signed-off-by: Jean Pihet <j-pihet@xxxxxx>
>> >> Signed-off-by: J Keerthy <j-keerthy@xxxxxx>
>> >> ---
>> >> arch/arm/mach-omap2/smartreflex.c | 12 ++++++------
>> >> include/linux/power/smartreflex.h | 23 ++++++++++++++++++++++-
>> >> 2 files changed, 28 insertions(+), 7 deletions(-)
>> >>
>> >> diff --git a/arch/arm/mach-omap2/smartreflex.c b/arch/arm/mach-omap2/smartreflex.c
>> >> index d859277..acef08d 100644
>> >> --- a/arch/arm/mach-omap2/smartreflex.c
>> >> +++ b/arch/arm/mach-omap2/smartreflex.c
>> >> @@ -289,9 +289,9 @@ static void sr_v1_disable(struct omap_sr *sr)
>> >> * Wait for SR to be disabled.
>> >> * wait until ERRCONFIG.MCUDISACKINTST = 1. Typical latency is 1us.
>> >> */
>> >> - omap_test_timeout((sr_read_reg(sr, ERRCONFIG_V1) &
>> >> - ERRCONFIG_MCUDISACKINTST), SR_DISABLE_TIMEOUT,
>> >> - timeout);
>> >> + sr_test_cond_timeout((sr_read_reg(sr, ERRCONFIG_V1) &
>> >> + ERRCONFIG_MCUDISACKINTST), SR_DISABLE_TIMEOUT,
>> >> + timeout);
>> >>
>> >> if (timeout >= SR_DISABLE_TIMEOUT)
>> >> dev_warn(&sr->pdev->dev, "%s: Smartreflex disable timedout\n",
>> >> @@ -334,9 +334,9 @@ static void sr_v2_disable(struct omap_sr *sr)
>> >> * Wait for SR to be disabled.
>> >> * wait until IRQSTATUS.MCUDISACKINTST = 1. Typical latency is 1us.
>> >> */
>> >> - omap_test_timeout((sr_read_reg(sr, IRQSTATUS) &
>> >> - IRQSTATUS_MCUDISABLEACKINT), SR_DISABLE_TIMEOUT,
>> >> - timeout);
>> >> + sr_test_cond_timeout((sr_read_reg(sr, IRQSTATUS) &
>> >> + IRQSTATUS_MCUDISABLEACKINT), SR_DISABLE_TIMEOUT,
>> >> + timeout);
>> >>
>> >> if (timeout >= SR_DISABLE_TIMEOUT)
>> >> dev_warn(&sr->pdev->dev, "%s: Smartreflex disable timedout\n",
>> >> diff --git a/include/linux/power/smartreflex.h b/include/linux/power/smartreflex.h
>> >> index 884eaee..78b795e 100644
>> >> --- a/include/linux/power/smartreflex.h
>> >> +++ b/include/linux/power/smartreflex.h
>> >> @@ -22,7 +22,7 @@
>> >>
>> >> #include <linux/types.h>
>> >> #include <linux/platform_device.h>
>> >> -
>> >> +#include <linux/delay.h>
>> >> #include <plat/voltage.h>
>> >>
>> >> /*
>> >> @@ -168,6 +168,27 @@ struct omap_sr {
>> >> };
>> >>
>> >> /**
>> >> + * test_cond_timeout - busy-loop, testing a condition
>> >> + * @cond: condition to test until it evaluates to true
>> >> + * @timeout: maximum number of microseconds in the timeout
>> >> + * @index: loop index (integer)
>> >> + *
>> >> + * Loop waiting for @cond to become true or until at least @timeout
>> >> + * microseconds have passed. To use, define some integer @index in the
>> >> + * calling code. After running, if @index == @timeout, then the loop has
>> >> + * timed out.
>> >> + *
>> >> + * Copied from omap_test_timeout */
>> >> +#define sr_test_cond_timeout(cond, timeout, index) \
>> >> +({ \
>> >> + for (index = 0; index < timeout; index++) { \
>> >> + if (cond) \
>> >> + break; \
>> >> + udelay(1); \
>> >> + } \
>> >> +})
>> >
>> > I think we can use time_after()/time_before() APIs for timeout and cpu_relax() for
>> > tight loops instead of udelay().
>>
>> cpu_relax() changes the priority everytime to low and will yield to
>> another thread.
>> Considering that we are checking the condition every microsecond does it make
>> some saving using cpu_relax().
>>
>
> cpu_relax() does not involve any priority changes or scheduling AFAICS.
> Have a look at this thread:
>
> http://www.spinics.net/lists/netdev/msg151699.html
Thanks. My bad. I meant yielding to another thread with in a space
of 1uS.
>
> Regards
> AnilKumar
>
--
Regards and Thanks,
Keerthy
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