From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacek Anaszewski Subject: Re: [PATCH v2 0/3] leds: blink resolution improvements Date: Wed, 29 Apr 2015 17:14:59 +0200 Message-ID: <5540F573.1040908@samsung.com> References: <553E6CF5.4030601@list.ru> <553F4B60.20204@samsung.com> <553F5CFF.9090601@list.ru> <553F83DC.8080701@samsung.com> <5540BFFD.4090205@list.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mailout3.w1.samsung.com ([210.118.77.13]:36000 "EHLO mailout3.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933223AbbD2PPD (ORCPT ); Wed, 29 Apr 2015 11:15:03 -0400 In-reply-to: <5540BFFD.4090205@list.ru> Sender: linux-leds-owner@vger.kernel.org List-Id: linux-leds@vger.kernel.org To: Stas Sergeev Cc: linux-leds@vger.kernel.org, Linux kernel , Stas Sergeev On 04/29/2015 01:26 PM, Stas Sergeev wrote: > 28.04.2015 15:58, Jacek Anaszewski =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> On 04/28/2015 12:12 PM, Stas Sergeev wrote: >>> 28.04.2015 11:57, Jacek Anaszewski =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >>>> 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 fro= m >> 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 &=3D ~SET_BRIGHTNESS_ASYNC; > led_cdev->flags |=3D 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. --=20 Best Regards, Jacek Anaszewski