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=-6.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, URIBL_BLOCKED,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 B1A79C43381 for ; Mon, 25 Mar 2019 08:48:38 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8309120863 for ; Mon, 25 Mar 2019 08:48:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="WS6iH7VO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8309120863 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=pengutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-amlogic-bounces+linux-amlogic=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=9U1QkyF6Ci62tEgpVah9vw41G7pyrGHOW3PYQejNgKw=; b=WS6iH7VO/AlJmr CAs366t7ZIrxNhJs+GS0x+2hzhjUVsRx84TH5E79HU5s6rSKkB7FvlrVHp5IKNgAyKjhk36jJwQPo HkRF9+kugiVrkXH9o3hDjNguaQoCm42/u2sZukDeEvjUas29nd2L6ulYeLSxtU3aSPQyij65DCoUg aSOAD5Wj+Yt+ZyEcpcz12P1jIlYLpWHm+fzPw3108fLfyH5VdnrcO4+lJRWxr5wULFxD2f+0PrKxT cvw6j4QibpT234QueI2KfvaGXJRYvXiHLnPKGODelGxNad168Ve4jVlXRPYqn6enFM9Iky2Qia9E+ PYeVLznrfOj2J+W9MhmQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1h8LHU-0002SR-8a; Mon, 25 Mar 2019 08:48:32 +0000 Received: from metis.ext.pengutronix.de ([2001:67c:670:201:290:27ff:fe1d:cc33]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1h8LHO-0002Ot-S1 for linux-amlogic@lists.infradead.org; Mon, 25 Mar 2019 08:48:31 +0000 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 1h8LHL-000192-E7; Mon, 25 Mar 2019 09:48:23 +0100 Received: from ukl by pty.hi.pengutronix.de with local (Exim 4.89) (envelope-from ) id 1h8LHK-0005lS-Pm; Mon, 25 Mar 2019 09:48:22 +0100 Date: Mon, 25 Mar 2019 09:48:22 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Martin Blumenstingl Subject: Re: [PATCH 1/1] pwm: meson: use the spin-lock only to protect register modifications Message-ID: <20190325084822.ozixel6bzi6xiw67@pengutronix.de> References: <20190324220217.15813-1-martin.blumenstingl@googlemail.com> <20190324220217.15813-2-martin.blumenstingl@googlemail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190324220217.15813-2-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-amlogic@lists.infradead.org X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190325_014827_094756_0E59FFE1 X-CRM114-Status: GOOD ( 14.02 ) X-BeenThere: linux-amlogic@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-pwm@vger.kernel.org, narmstrong@baylibre.com, linux-kernel@vger.kernel.org, thierry.reding@gmail.com, linux-amlogic@lists.infradead.org, linux-arm-kernel@lists.infradead.org, jbrunet@baylibre.com Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-amlogic" Errors-To: linux-amlogic-bounces+linux-amlogic=archiver.kernel.org@lists.infradead.org Hello, On Sun, Mar 24, 2019 at 11:02:17PM +0100, Martin Blumenstingl wrote: > Holding the spin-lock for all of the code in meson_pwm_apply() can > result in a "BUG: scheduling while atomic". This can happen because > clk_get_rate() (which is called from meson_pwm_calc()) may sleep. > Only hold the spin-lock when modifying registers to solve this. > = > The reason why we need a spin-lock in the driver is because the > REG_MISC_AB register is shared between the two channels provided by one > PWM controller. The only functions where REG_MISC_AB is modified are > meson_pwm_enable() and meson_pwm_disable() so the register reads/writes > in there need to be protected by the spin-lock. > = > The original code also used the spin-lock to protect the values in > struct meson_pwm_channel. This could be necessary if two consumers can > use the same PWM channel. However, PWM core doesn't allow this so we > don't need to protect the values in struct meson_pwm_channel with a > lock. > = > Fixes: 211ed630753d2f ("pwm: Add support for Meson PWM Controller") > Signed-off-by: Martin Blumenstingl Looks right. Reviewed-by: Uwe Kleine-K=F6nig Bonus points for adding a comment to struct meson_pwm::lock. Something like: /* * Protects register access to the MISC_AB register that is * shared between the two PWMs. */ Best regards Uwe -- = Pengutronix e.K. | Uwe Kleine-K=F6nig | Industrial Linux Solutions | http://www.pengutronix.de/ | _______________________________________________ linux-amlogic mailing list linux-amlogic@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-amlogic