From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752130AbbD3RLr (ORCPT ); Thu, 30 Apr 2015 13:11:47 -0400 Received: from smtp5.mail.ru ([94.100.179.24]:34656 "EHLO smtp5.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751086AbbD3RLq (ORCPT ); Thu, 30 Apr 2015 13:11:46 -0400 Message-ID: <5542624D.70701@list.ru> Date: Thu, 30 Apr 2015 20:11:41 +0300 From: Stas Sergeev User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Jacek Anaszewski CC: linux-leds@vger.kernel.org, Linux kernel , Stas Sergeev Subject: Re: [PATCH v2 0/3] leds: blink resolution improvements References: <553E6CF5.4030601@list.ru> <553F4B60.20204@samsung.com> <553F5CFF.9090601@list.ru> <553F83DC.8080701@samsung.com> In-Reply-To: <553F83DC.8080701@samsung.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Spam: Not detected X-Mras: Ok Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 28.04.2015 15:58, Jacek Anaszewski пишет: >>> 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 drivers, >>> 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've now found that the drivers itself use a work queue when needed. And some drivers, like leds_gpio, even do this: --- if (led_dat->can_sleep) { led_dat->new_level = level; schedule_work(&led_dat->work); } else { set_brightness_now(); } --- So it seems the problem is already solved on the per-driver basis. I don't have leds-aat1290 driver, it is probably not in the kernel. It is likely forgetting to use the work-queue the way all other drivers do. So I think my patch is good for the in-kernel drivers. There is also a led_cdev->set_brightness_work, and it looks unused. I could use it for my patch, but for what, if the drivers already use the work queue when needed?