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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 5CEE4C43381 for ; Mon, 25 Mar 2019 08:42:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2BC8C20830 for ; Mon, 25 Mar 2019 08:42:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730116AbfCYImH (ORCPT ); Mon, 25 Mar 2019 04:42:07 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:46779 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729920AbfCYImH (ORCPT ); Mon, 25 Mar 2019 04:42:07 -0400 Received: from pty.hi.pengutronix.de ([2001:67c:670:100:1d::c5]) by metis.ext.pengutronix.de with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1h8LB4-0000Dm-Ks; Mon, 25 Mar 2019 09:41:54 +0100 Received: from ukl by pty.hi.pengutronix.de with local (Exim 4.89) (envelope-from ) id 1h8LB3-0005Ss-Rx; Mon, 25 Mar 2019 09:41:53 +0100 Date: Mon, 25 Mar 2019 09:41:53 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Martin Blumenstingl Cc: thierry.reding@gmail.com, narmstrong@baylibre.com, jbrunet@baylibre.com, linux-pwm@vger.kernel.org, linux-amlogic@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/1] pwm: meson: fix scheduling while atomic issue Message-ID: <20190325084153.l44pzfewcqlkoaoe@pengutronix.de> References: <20190324220217.15813-1-martin.blumenstingl@googlemail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190324220217.15813-1-martin.blumenstingl@googlemail.com> User-Agent: NeoMutt/20170113 (1.7.2) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c5 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Martin, On Sun, Mar 24, 2019 at 11:02:16PM +0100, Martin Blumenstingl wrote: > Back in January a "BUG: scheduling while atomic" error showed up during > boot on my Meson8b Odroid-C1 (which uses a PWM regulator as CPU supply). > The call trace comes down to: > __mutex_lock > clk_prepare_lock > clk_core_get_rate > meson_pwm_apply > .. > dev_pm_opp_set_rate > .. > > Jerome has also seen the same problem but from pwm-leds (instead of a > pwm-regulator). He posted a patch which replaces the spinlock with a > mutex. That works. I believe we can optimize this by reducing the time > where the lock is held - that also allows to keep the spin-lock. > > Analyzing this issue helped me understand the pwm-meson driver better. > My plan is to send some cleanups (with the goal of re-using more of the > goodies from the PWM core in the pwm-meson driver) after this single fix > is merged (they can be found here: [1]). I didn't look over these in detail, but I see an issue that according to the shortlogs isn't addressed: In the .apply callback there is (simplified): if (!state->enabled) { meson_pwm_disable(meson, pwm->hwpwm); return; } This results in the wrong output after: pwm_apply_state(pwm, { .enabled = true, .polarity = PWM_POLARITY_NORMAL, ...}); pwm_apply_state(pwm, { .enabled = false, .polarity = PWM_POLARITY_INVERTED, ...}); because the polarity isn't checked. If you want to implement further cleanups, my questions and propositions are: - Is there a publicly available manual for this hardware? If yes, you can add a link to it in the header of the driver. - Why do you handle reparenting of the PWM's clk in .request? Wouldn't this be more suitable in .apply? - Does stopping the PWM (i.e. clearing MISC_{A,B}_EN in the MISC_AB register) freeze the output, or is the currently running period completed first? (The latter is the right behaviour.) - Please point out in the header that for changing period/duty cycle/polarity the hardware must be stopped. (I suggest to apply the style used in https://www.spinics.net/lists/linux-pwm/msg09262.html for some consistency.) Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |