From patchwork Wed Dec 17 10:51:11 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sjoerd Simons X-Patchwork-Id: 422231 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 066C014010F for ; Wed, 17 Dec 2014 21:51:18 +1100 (AEDT) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751163AbaLQKvR (ORCPT ); Wed, 17 Dec 2014 05:51:17 -0500 Received: from bhuna.collabora.co.uk ([93.93.135.160]:40348 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751068AbaLQKvQ (ORCPT ); Wed, 17 Dec 2014 05:51:16 -0500 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: sjoerd) with ESMTPSA id D615B600695 Received: by dusk.luon.net (Postfix, from userid 1000) id AD7C02233F; Wed, 17 Dec 2014 11:51:11 +0100 (CET) From: Sjoerd Simons To: Thierry Reding Cc: linux-pwm@vger.kernel.org, Ajay Kumar , Tomasz Figa , Javier Martinez Canillas , inux-samsung-soc@vger.kernel.org Subject: [PATCH] pwm: samsung: Fix output race on disabling Date: Wed, 17 Dec 2014 11:51:11 +0100 Message-Id: <1418813471-14962-1-git-send-email-sjoerd.simons@collabora.co.uk> X-Mailer: git-send-email 2.1.3 Sender: linux-pwm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pwm@vger.kernel.org When disabling the samsung PWM the output state remains at the level it was in the end of a pwm cycle. In other words, calling pwm_disable when at 100% duty will keep the output active, while at all other setting the output will go/stay inactive. On top of that the samsung PWM settings are double-buffered, which means the new settings only get applied at the start of a new PWM cycle. This results in a race if the PWM is at 100% duty and a driver calls: pwm_config (pwm, 0, period); pwm_disable (pwm); In this case the PWMs output will unexpectedly stay active, unless a new PWM cycle happened to start between the register writes in _config and _disable. As far as i can tell this is a regression introduced by 3bdf878, before that a call to pwm_config would call pwm_samsung_enable which, while heavy-handed, made sure the expected settings were live. To resolve this, while not re-introducing the issues 3bdf878 (flickering as the PWM got reset while in a PWM cycle). Only force an update of the settings when at 100% duty, which shouldn't have a noticeable effect on the output but is enough to ensure the behaviour is as expected on disable. Signed-off-by: Sjoerd Simons --- drivers/pwm/pwm-samsung.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c index 3e9b583..3e252dc 100644 --- a/drivers/pwm/pwm-samsung.c +++ b/drivers/pwm/pwm-samsung.c @@ -335,6 +335,27 @@ static int pwm_samsung_config(struct pwm_chip *chip, struct pwm_device *pwm, writel(tcnt, our_chip->base + REG_TCNTB(pwm->hwpwm)); writel(tcmp, our_chip->base + REG_TCMPB(pwm->hwpwm)); + /* In case the PWM is currently at 100% duty, trigger a manual update to + * prevent unexpected results when disabling the pwm */ + if (chan->period_ns/chan->tin_ns == chan->duty_ns/chan->tin_ns) { + unsigned int tcon_chan = to_tcon_channel(pwm->hwpwm); + u32 tcon; + unsigned long flags; + + dev_dbg(our_chip->chip.dev, "Forcing manual update"); + + spin_lock_irqsave(&samsung_pwm_lock, flags); + + tcon = readl(our_chip->base + REG_TCON); + tcon |= TCON_MANUALUPDATE(tcon_chan); + writel(tcon, our_chip->base + REG_TCON); + + tcon &= ~TCON_MANUALUPDATE(tcon_chan); + writel(tcon, our_chip->base + REG_TCON); + + spin_unlock_irqrestore(&samsung_pwm_lock, flags); + } + chan->period_ns = period_ns; chan->tin_ns = tin_ns; chan->duty_ns = duty_ns;