28.04.2015 15:58, Jacek Anaszewski ÐÐÑÐÑ:
On 04/28/2015 12:12 PM, Stas Sergeev wrote:Why such a complexity?
28.04.2015 11:57, Jacek Anaszewski ÐÐÑÐÑ:Please take into account that this could work reliably only for gpio
Hi Stas,Of course I did.
Have you tested it?
Works with gpio driver and provides up to 10usec precision on
This is 1000 times better than without my patch - the precision
was 10ms (jiffy).
LEDs. For the LEDs driven though a bus (e.g. I2C) delays below 1ms
might be hard to achieve. The minimum available delay would vary from
driver to driver.
We could think of adding the hr_timer mode to the led-class.
The mode could be turned on with use of a new led_set_high_res_timer
API. The API would be called by drivers/leds/leds-gpio.c driver when
a dedicated sysfs attribute was set adequately.
The other drivers could also set this mode if they controlled device
with a suitable LED switching rate. The minimum delay value could
be made configurable by the driver and readable through sysfs
when in hr_timer mode.
Wouldn't it be enough if the driver can set the minimum delay
value, yet to always use the hrtimer?
Please note that 10ms (jiffy) is an inadequate minimum delay
pretty much for any driver, I guess. At least 1ms should be possible,
because, well, you can write 1ms to sysfs attribute even without
my patch. So even the existing options need hrtimer to work right.
I think I should try a tasklet then.usec also didn't work, please look at my use case and warning:I tried it with Samsung M0 board andOK, I can remove the nsec resolution.
my leds-aat1290 driver. It didn't work well. And for small delay
intervals it will not have a chance to work reliably with all drivers,
especially the ones which use mutex in their brightness_set op,
since mutex can sleep.
echo "timer" > trigger
echo 1 > delay_on
echo 1 > delay_off
echo usec > delay_unit
[ 178.584433] hrtimer: interrupt took 300747 ns
Only some time later I realized that for AAT1290 brightness is setOK, so we need a tasklet and the ability for the driver to set the
through ASCwire pulse protocol, which takes few ms.
Please note that with this approach users would have to wonder why
they are getting the warnings and why they can't get their LEDs to work
with given settings.
minimal delay. I think I can implement the former and hope someone
else will later implement the later. :)
Lets just solve the problem step-by-step. I can't solve all the
problems at once, but you can't deny the fact that the problem
exists and needs to be solved.