From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A89ABC47404 for ; Wed, 9 Oct 2019 10:19:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8A33E20673 for ; Wed, 9 Oct 2019 10:19:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730823AbfJIKTp (ORCPT ); Wed, 9 Oct 2019 06:19:45 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:58898 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725935AbfJIKTo (ORCPT ); Wed, 9 Oct 2019 06:19:44 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: eballetbo) with ESMTPSA id 3236C28F6C7 Subject: Re: [PATCH] pwm: cros-ec: Let cros_ec_pwm_get_state() return the last applied state To: =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= , Daniel Thompson Cc: linux-kernel@vger.kernel.org, thierry.reding@gmail.com, heiko@sntech.de, dianders@chromium.org, mka@chromium.org, groeck@chromium.org, kernel@collabora.com, bleung@chromium.org, linux-pwm@vger.kernel.org, Lee Jones References: <20191008105417.16132-1-enric.balletbo@collabora.com> <20191008143432.pbhcqamd6f4qwbqn@pengutronix.de> <4f009344-242e-19a7-6872-2c55df086044@collabora.com> <20191008203137.s22clq6v2om5ktio@pengutronix.de> <53b7d02b-1a2d-11da-fdd0-5378f360d876@collabora.com> <20191009095635.yysr33lnwldicyng@holly.lan> <20191009101637.gmvghwdvcmfw4yyk@pengutronix.de> From: Enric Balletbo i Serra Message-ID: <2b24df87-10fb-f590-3643-ffca5f180f5d@collabora.com> Date: Wed, 9 Oct 2019 12:19:38 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191009101637.gmvghwdvcmfw4yyk@pengutronix.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 9/10/19 12:16, Uwe Kleine-König wrote: > On Wed, Oct 09, 2019 at 10:56:35AM +0100, Daniel Thompson wrote: >> On Wed, Oct 09, 2019 at 11:27:13AM +0200, Enric Balletbo i Serra wrote: >>> Hi Uwe, >>> >>> Adding Daniel and Lee to the discussion ... >> >> Thanks! >> >>> On 8/10/19 22:31, Uwe Kleine-König wrote: >>>> On Tue, Oct 08, 2019 at 06:33:15PM +0200, Enric Balletbo i Serra wrote: >>>>>> A few thoughts to your approach here ...: >>>>>> >>>>>> - Would it make sense to only store duty_cycle and enabled in the >>>>>> driver struct? >>>>>> >>>>> >>>>> Yes, in fact, my first approach (that I didn't send) was only storing enabled >>>>> and duty cycle. For some reason I ended storing the full pwm_state struct, but I >>>>> guess is not really needed. >>>>> >>>>> >>>>>> - Which driver is the consumer of your pwm? If I understand correctly >>>>>> the following sequence is the bad one: >>>>>> >>>>> >>>>> The consumer is the pwm_bl driver. Actually I'n trying to identify >>>>> other consumers. >>>> >>> >>> So far, the pwm_bl driver is the only consumer of cros-ec-pwm. >>> >>>> Ah, I see why I missed to identify the problem back when I checked this >>>> driver. The problem is not that .duty_cycle isn't set but there .enabled >>>> isn't set. So maybe we just want: >>>> >>>> diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c >>>> index 2201b8c78641..0468c6ee4448 100644 >>>> --- a/drivers/video/backlight/pwm_bl.c >>>> +++ b/drivers/video/backlight/pwm_bl.c >>>> @@ -123,6 +123,7 @@ static int pwm_backlight_update_status(struct backlight_device *bl) >>>> if (brightness > 0) { >>>> pwm_get_state(pb->pwm, &state); >>>> state.duty_cycle = compute_duty_cycle(pb, brightness); >>>> + state.enabled = true; >>>> pwm_apply_state(pb->pwm, &state); >>>> pwm_backlight_power_on(pb); >>>> } else >>>> >>>> ? On a side note: It's IMHO strange that pwm_backlight_power_on >>>> reconfigures the PWM once more. >>>> >>> >>> Looking again to the pwm_bl code, now, I am not sure this is correct (although >>> it probably solves the problem for me). >> >> Looking at the pwm_bl code I wouldn't accept the above as it is but I'd >> almost certainly accept a patch to pwm_bl to move the PWM enable/disable >> out of both the power on/off functions so the duty-cycle/enable or >> disable can happen in one go within the update_status function. I don't >> think such a change would interfere with the power and enable sequencing >> needed by panels and it would therefore be a nice continuation of the >> work to convert over to the pwm_apply_state() API. > > OK for me. Enric, do you care enough to come up with a patch for pwm_bl? > I'd expect that this alone should already fix your issue. > Yes, I'll work on a proposal and send. Thanks you all. Regards, Enric >> None of the above has anything to do with what is right or wrong for >> the PWM API evolution. Of course, if this thread does conclude that it >> is OK the duty cycle of a disabled PWM to be retained for some drivers >> and not others then I'd hope to see some WARN_ON()s added to the PWM >> framework to help bring problems to the surface with all drivers. > > I think it's not possible to add a reliable WARN_ON for that issue. It > is quite expected that .get_state returns something that doesn't > completely match the requested configuration. So if a consumer requests > > .duty_cycle = 1 > .period = 100000000 > .enabled = false > > pwm_get_state possibly returns .duty_cycle = 0 even for drivers/hardware > that has a concept of duty_cycle for disabled hardware. > > A bit this is addressed in https://patchwork.ozlabs.org/patch/1147517/. > > Best regards > Uwe >