From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anand Moon Subject: [PATCH 5/6] pwm: samsung: Fix output race on disabling Date: Fri, 27 Mar 2015 03:09:14 +1030 Message-ID: <1427387955-5129-6-git-send-email-linux.amoon@gmail.com> References: <1427387955-5129-1-git-send-email-linux.amoon@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1427387955-5129-1-git-send-email-linux.amoon@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Lukasz Majewski , Eduardo Valentin , Sjoerd Simons , Russell King , Kukjin Kim Cc: devicetree@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-pwm@vger.kernel.org, Anand Moon , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org From: Sjoerd Simons 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 Signed-off-by: Anand Moon --- drivers/pwm/pwm-samsung.c | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) diff --git a/drivers/pwm/pwm-samsung.c b/drivers/pwm/pwm-samsung.c index 3e9b583..649f6c4 100644 --- a/drivers/pwm/pwm-samsung.c +++ b/drivers/pwm/pwm-samsung.c @@ -269,12 +269,31 @@ static void pwm_samsung_disable(struct pwm_chip *chip, struct pwm_device *pwm) spin_unlock_irqrestore(&samsung_pwm_lock, flags); } +static void pwm_samsung_manual_update(struct samsung_pwm_chip *chip, + struct pwm_device *pwm) +{ + unsigned int tcon_chan = to_tcon_channel(pwm->hwpwm); + u32 tcon; + unsigned long flags; + + spin_lock_irqsave(&samsung_pwm_lock, flags); + + tcon = readl(chip->base + REG_TCON); + tcon |= TCON_MANUALUPDATE(tcon_chan); + writel(tcon, chip->base + REG_TCON); + + tcon &= ~TCON_MANUALUPDATE(tcon_chan); + writel(tcon, chip->base + REG_TCON); + + spin_unlock_irqrestore(&samsung_pwm_lock, flags); +} + static int pwm_samsung_config(struct pwm_chip *chip, struct pwm_device *pwm, int duty_ns, int period_ns) { struct samsung_pwm_chip *our_chip = to_samsung_pwm_chip(chip); struct samsung_pwm_channel *chan = pwm_get_chip_data(pwm); - u32 tin_ns = chan->tin_ns, tcnt, tcmp; + u32 tin_ns = chan->tin_ns, tcnt, tcmp, oldtcmp; /* * We currently avoid using 64bit arithmetic by using the @@ -288,6 +307,7 @@ static int pwm_samsung_config(struct pwm_chip *chip, struct pwm_device *pwm, return 0; tcnt = readl(our_chip->base + REG_TCNTB(pwm->hwpwm)); + oldtcmp = readl(our_chip->base + REG_TCMPB(pwm->hwpwm)); /* We need tick count for calculation, not last tick. */ ++tcnt; @@ -335,6 +355,15 @@ 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, force a manual update + * to prevent the signal staying high in the pwm is disabled shortly + * afer this update (before it autoreloaded the new values) . + */ + if (oldtcmp == (u32) -1) { + dev_dbg(our_chip->chip.dev, "Forcing manual update"); + pwm_samsung_manual_update(our_chip, pwm); + } + chan->period_ns = period_ns; chan->tin_ns = tin_ns; chan->duty_ns = duty_ns; -- 1.9.1