Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754494AbcKNMvt (ORCPT ); Mon, 14 Nov 2016 07:51:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:60184 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753791AbcKNMvq (ORCPT ); Mon, 14 Nov 2016 07:51:46 -0500 Subject: Re: PM regression with LED changes in next-20161109 To: Jacek Anaszewski , Jacek Anaszewski , Pavel Machek References: <20161109192301.GS26979@atomide.com> <28234714-3994-6747-9cf8-1ff0b3257f7a@gmail.com>

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<9b476f85-d45e-deb6-335d-fc56f6d90350@redhat.com> <127cdd42-6fd8-c671-60b7-3826b351577f@samsung.com> Cc: Tony Lindgren , linux-leds@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Darren Hart From: Hans de Goede Message-ID: <15cafbf5-d842-e184-2fd4-65f8272f505a@redhat.com> Date: Mon, 14 Nov 2016 13:51:41 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <127cdd42-6fd8-c671-60b7-3826b351577f@samsung.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Mon, 14 Nov 2016 12:51:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6622 Lines: 166 Hi, On 14-11-16 10:12, Jacek Anaszewski wrote: > Hi, > > On 11/13/2016 02:52 PM, Hans de Goede wrote: >> Hi, >> >> On 13-11-16 12:44, Jacek Anaszewski wrote: >>> Hi, >>> >>> On 11/12/2016 10:14 PM, Hans de Goede wrote: >> >> >> >>>>>> So I would like to propose creating a new read-write >>>>>> user_brightness file. >>>>>> >>>>>> The write behavior would be 100% identical to the brightness >>>>>> file (in code terms it will call the same store function). >>>>>> >>>>>> The the read behavior otoh will be different: it will shows >>>>>> the last brightness as set by the user, this would show the >>>>>> read behavior we really want of brightness: show the real >>>>>> brightness when not blinking / triggers are active and show >>>>>> the brightness used when on when blinking / triggers are active. >>>>>> >>>>>> We could then add poll support on this new user_brightness >>>>>> file, thus avoiding the problem with the extra cpu-load on >>>>>> notifications on blinking / triggers. >>>>> >>>>> I agree that user_brightness allows to solve the issues you raised >>>>> about inconsistent write and read brightness' semantics >>>>> (which is not that painful IMHO). >>>>> >>>>> Reporting non-user brightness changes on user_brightness file >>>>> doesn't sound reasonable though. >>>> >>>> The changes I'm interested in are user brightness changes they >>>> are just not done through sysfs, but through a hardwired hotkey, >>>> they are however very much done by the user. >>> >>> Ah, so this file name would be misleading especially taking into account >>> the context in which "user" is used in kernel, which predominantly >>> means "userspace", e.g. copy_to_user(), copy_from_user(). >>> >>>>> Also, how would we read the >>>>> brightness set by the firmware? We'd have to read brightness >>>>> file, so still two files would have to be opened which is >>>>> a second drawback of this approach. >>>> >>>> No, look carefully at the definition of the read behavior >>>> I plan to put in the ABI doc: >>> >>> OK, "user" was what confused me. So in this case changes made >>> by the firmware even if in a result of user activity >>> (pressing hardware key) obviously cannot be treated similarly >>> to the changes made from the userspace context. >> >> In the end both result on the brightness of the device >> changing, so any userspace process interested in monitoring >> the brightness will want to know about both type of changes. >> >>> Unless you're able to give references to the kernel code which >>> contradict my judgement. >> >> AFAIK the audio code will signal volume changes done by >> hardwired buttons the same way as audio changes done >> by userspace calling into the kernel. This also makes >> sense because in the end, what is interesting for a >> mixer app, is that the volume changed, and what the >> new volume is. > > OK, so it is indeed similar to your LED use case. Nonetheless > in case of LED controllers it is also possible that hardware > adjusts LED brightness in case of low battery voltage. > > If a device is able e.g. to generate an interrupt to notify this > kind of event, then we would like also to be able to notify the client > about that. It wouldn't be user generated brightness change though. > >>>> "Reading this file will return the actual led brightness >>>> when not blinking and no triggers are active; reading this >>>> file will return the brightness used when the led is on >>>> when blinking or triggers are active." >>> >>> This is unnecessarily entangled. Blinking means timer trigger >>> is active. >> >> Ok. >> >>>> So for e.g. the backlit keyboard case reading this single >>>> file will return the actual brightness of the backlight, >>>> since this does not involve blinking or triggers. >>>> >>>> Basically the idea is that the user_brightness file >>>> will have the semantics which IMHO the brightness file >>>> itself should have had from the beginning, but which >>>> we can't change now due to ABI reasons. >>> >>> And in fact introducing user_brightness file would indeed >>> fix that shortcoming. However without providing notifications >>> of hw brightness changes on it. >> >> See above, I believe such a file should report any >> changes in brightness, except those caused by triggers, >> so it would report hw brightness changes. >> >> Anyways if you're not interested in fixing the >> shortcomings of the current read behavior on the >> brightness file (I'm fine with that, I can live >> with the shortcomings) I suggest that we simply go >> with v2 of my poll() patch. > > v2 entails power consumption related issues. > > Generally I think that we could add the file you proposed, > however it would be good to devise a name which will cover > also the cases when brightness is changed by firmware without > user interaction. > >>>>> Having no difference in this area between the two approaches >>>>> I'm still in favour of the read-only file for notifying >>>>> brightness changes procured by hardware. >>>> >>>> That brings back the needing 2 fds problem; and does >>>> not solve userspace not being able to reliably read >>>> the led on brightness when blinking or using triggers. >>>> >>>> And this also has the issue that one is doing poll() on >>>> one fd to detect changes on another fd, >>> >>> It is not necessarily true. We can treat the polling on >>> hw_brightness_change file as a means to detect brightness >>> changes procured by hardware and we can read that brightness >>> by executing read on this same fd. It could return -ENODATA >>> if no such an event has occurred so far. >> >> That would still require 2 fds as userspace also wants to >> be able to set the keyboard backlight, but allowing read() >> on the hw_brightness_change file at least fixes the weirdness >> where userspace gets woken from poll() without being able to >> read. So if you insist on going the hw_brightness_change file >> route, then I can live with that (and upower will simply >> need to open 2 fds, that is doable). >> >> But, BUT, I would greatly prefer to just go for v4 of my >> patch, which fixes the only real problem we've seen with >> my patch as original merged without adding a new, somewhat >> convoluted sysfs attribute. > > Hmm, v4 still calls led_notify_brightness_change(led_cdev) > from both __led_set_brightness() and __led_set_brightness_blocking(). Ugh, I see I accidentally send a v4 twice, instead of calling the version which dropped those called v5 as I should have, sorry. The v4 which I would like to see merged, the one with those calls dropped, is here: https://patchwork.kernel.org/patch/9423093/ Regards, Hans