Messages in this thread | | | Date | Wed, 29 Apr 2015 17:14:59 +0200 | From | Jacek Anaszewski <> | Subject | Re: [PATCH v2 0/3] leds: blink resolution improvements |
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On 04/29/2015 01:26 PM, Stas Sergeev wrote: > 28.04.2015 15:58, Jacek Anaszewski пишет: >> On 04/28/2015 12:12 PM, Stas Sergeev wrote: >>> 28.04.2015 11:57, Jacek Anaszewski пишет: >>>> Hi Stas, >>>> >>>> Have you tested it? >>> Of course I did. >>> Works with gpio driver and provides up to 10usec precision on >>> armada-xp board. >>> This is 1000 times better than without my patch - the precision >>> was 10ms (jiffy). >> >> Please take into account that this could work reliably only for gpio >> 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. > I've found the SET_BRIGHTNESS_ASYNC and SET_BRIGHTNESS_SYNC flags. > Sounds interesting for my patch, but the only "documentation" I was > able to find, is this: > --- > /* Setting a torch brightness needs to have immediate effect */ > led_cdev->flags &= ~SET_BRIGHTNESS_ASYNC; > led_cdev->flags |= SET_BRIGHTNESS_SYNC; > --- > Aren't these flags mutually exclusive, and so just one could have > been used?
Yes they are.
> Anyway, from that comment I can try to guess that if the driver > supports ASYNC mode, it should be fast enough and without sleeps. > The drivers that do i2c transfers with sleeps, should be using SYNC > mode. Or was the intention for these flags entirely different?
Sync mode was designed for flash LED devices, for which turning torch immediately has a big importance because they are often synchronized with camera sensor.
Triggers use led_set_brightness_async API anyway.
> My intention is to use either a work-queue or a direct hrtimer > callback, depending on whether the driver supports sync or async > mode. This is instead of the driver being able to set the minimum > delay - much simpler to implement. Makes sense? > Can I use the above flags for that purpose, or will I need > a new one? >
These flags are intended for internal LED core use.
-- Best Regards, Jacek Anaszewski
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