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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7022CE92710 for ; Thu, 5 Oct 2023 14:09:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232774AbjJEOJh (ORCPT ); Thu, 5 Oct 2023 10:09:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40696 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232778AbjJEOHY (ORCPT ); Thu, 5 Oct 2023 10:07:24 -0400 Received: from gofer.mess.org (gofer.mess.org [IPv6:2a02:8011:d000:212::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9CCF08A71; Thu, 5 Oct 2023 01:30:38 -0700 (PDT) Received: by gofer.mess.org (Postfix, from userid 1000) id EFC201007F6; Thu, 5 Oct 2023 09:30:32 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mess.org; s=2020; t=1696494632; bh=yTqM0lOviMpVtY3gEC2fnjg+lpnZmaa/xqOOO1oFjzg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hM4/6PU/BVCUmsjcFfLAZHOdsLJZBPi+IERfvAziz3nfnEK4C7KS4IvaOhQF74oUa pm/jySTmFQfMxdTKCSDifYiz+6AUgqHrAipeZA/gPtdfM+zALHVTx2Zc3etj0F8Uvj Z+6+P3UfUXB4S+dg6826xd+d4QJrSOPKQf4pOCA+1cpbIPfgjobt3K8v8W29gu2XFf EozsFhCZzdMkmYxxlZzWuHs3+awRG8hRctGYRXzu5lggSBZ9V8y5NfKjZIp5utFREo m8TSihVOCaoYFaigu8xqW/v53d8h8T2slqaY2mkHTgDaQkYnFk+bb6M8VNQI8mAzW8 t0IV4IH911NYA== Date: Thu, 5 Oct 2023 09:30:32 +0100 From: Sean Young To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: Thierry Reding , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team , Vladimir Zapolskiy , Conor Dooley , Daire McNamara , Palmer Dabbelt , Paul Walmsley , Fabrice Gasnier , Maxime Coquelin , Alexandre Torgue , linux-pwm@vger.kernel.org, Ivaylo Dimitrov , linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 1/2] pwm: make it possible to apply pwm changes in atomic context Message-ID: References: <1bd5241d584ceb4d6b731c4dc3203fb9686ee1d1.1696156485.git.sean@mess.org> <20231004095920.ne7yrrthow6tnuvg@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20231004095920.ne7yrrthow6tnuvg@pengutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Uwe, On Wed, Oct 04, 2023 at 11:59:20AM +0200, Uwe Kleine-König wrote: > On Sun, Oct 01, 2023 at 11:40:29AM +0100, Sean Young wrote: > > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c > > index dc66e3405bf5..d9679ae5b2be 100644 > > --- a/drivers/pwm/core.c > > +++ b/drivers/pwm/core.c > > @@ -505,7 +505,7 @@ int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state) > > * is a bad idea. So make it explicit that calling this function might > > * sleep. > > */ > > - might_sleep(); > > + might_sleep_if(pwm_can_sleep(pwm)); > > > > if (!pwm || !state || !state->period || > > state->duty_cycle > state->period) > > I'd like to have a mechanism to catch drivers that missed to set > .can_sleep. The best idea I currently have for that is to disable > preemption if IS_ENABLED(CONFIG_PWM_DEBUG) && !pwm_can_sleep(pwm) while > .apply() is running. If we have pwm_apply_state_atomic(), then CONFIG_DEBUG_ATOMIC_SLEEP will catch them, but only in that code path of course. How about using non_block_start() and non_block_end() if can_sleep is not set? > > diff --git a/drivers/pwm/pwm-fsl-ftm.c b/drivers/pwm/pwm-fsl-ftm.c > > index b7c6045c5d08..b8b9392844e9 100644 > > --- a/drivers/pwm/pwm-fsl-ftm.c > > +++ b/drivers/pwm/pwm-fsl-ftm.c > > @@ -405,6 +405,7 @@ static int fsl_pwm_probe(struct platform_device *pdev) > > > > fpc->soc = of_device_get_match_data(&pdev->dev); > > fpc->chip.dev = &pdev->dev; > > + fpc->chip.can_sleep = true; > > As .apply() being callable in non-sleepable context only depends on > .apply() I think a better place for this property is in struct pwm_ops. That makes sense. > Also I wonder if the distinction between atomic and sleeping > pwm_state_apply() should be more explicit. For GPIOs you have a sleeping > variant gpiod_set_value_cansleep() that allows to immediately determine > the intended context in the caller. This would allow that programming > a PWM stays a preemption point (if possible/desired) even if the > underlying hardware/driver is atomic. To not have to touch all consumer > drivers, maybe the pair for pwm should better be > > pwm_apply_state() > pwm_apply_state_atomic() Do we need pwm_config_atomic(), pwm_enable_atomic(), and pwm_disable_atomic() too? These are just convenience functions, so we can probably do without them. > instead of a "cansleep" suffix for the sleeping variant? Or maybe it's > better to accept touching all consumer drivers to get semantics similar > to gpio? I couldn't decide quickly what I really like better here, so > that's your chance to comment and influence the outcome :-) If you expect to have more parameters for pwm_apply_state() then a flags argument makes sense. TBH I like the pwm_apply_state_atomic() option. Sean