Re: [PATCH] drm/i915: use hrtimer in wait for vblank

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 24 Mar 2014, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> On Mon, Mar 24, 2014 at 01:43:38PM +0530, Arun R Murthy wrote:
>> In wait for vblank use usleep_range, which will use hrtimers instead of
>> msleep. Using msleep(1~20) there are more chances of sleeping for 20ms.
>> Using usleep_range uses hrtimers and hence are precise, worst case will
>> trigger an interrupt at the higher/max timeout.
>> 
>> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_drv.h |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
>> index 44067bc..079280a 100644
>> --- a/drivers/gpu/drm/i915/intel_drv.h
>> +++ b/drivers/gpu/drm/i915/intel_drv.h
>> @@ -52,7 +52,7 @@
>>  			break;						\
>>  		}							\
>>  		if (W && drm_can_sleep())  {				\
>> -			msleep(W);					\
>> +			usleep_range(W * 1000, W * 2 * 1000);		\
>>  		} else {						\
>>  			cpu_relax();					\
>>  		}							\
>
> Ok. But W is still just a random value we picked for being the mininum
> legal value for msleep(). So just usleep_range(500, 2000) or somesuch
> will be fine. We can rename W to CAN_SLEEP it that helps.

We do use _wait_for directly from intel_dp.c with W == 10 to not retry
so many times on what's expected to be a long wait.

BR,
Jani.


> -Chris
>
> -- 
> Chris Wilson, Intel Open Source Technology Centre

-- 
Jani Nikula, Intel Open Source Technology Center