From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacek Anaszewski Subject: Re: [PATCH v2 0/3] leds: blink resolution improvements Date: Tue, 28 Apr 2015 14:58:04 +0200 Message-ID: <553F83DC.8080701@samsung.com> References: <553E6CF5.4030601@list.ru> <553F4B60.20204@samsung.com> <553F5CFF.9090601@list.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mailout2.w1.samsung.com ([210.118.77.12]:41189 "EHLO mailout2.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965513AbbD1M6I (ORCPT ); Tue, 28 Apr 2015 08:58:08 -0400 In-reply-to: <553F5CFF.9090601@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 04/28/2015 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 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 tried it with Samsung M0 board and >> 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 driver= s, >> especially the ones which use mutex in their brightness_set op, >> since mutex can sleep. > OK, I can remove the nsec resolution. usec also didn't work, please look at my use case and warning: 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 set 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. > I added it for the future, it doesn't work for me either, but > hrtimer has an API for it, so I thought it may work on another hw. > I don't see why it can't stay, but if it bothers you that much, > I'll remove it. > >> I am afraid that we have to stay with what we have currently. > This is a counter-productive conclusion. > > My patch does 1000 times precision improvement with gpio driver. > If you only want nsec to be removed as it doesn't work - that's > fine with me. > --=20 Best Regards, Jacek Anaszewski