From d7541cb8df432cc60676f1be6d59044d944151e8 Mon Sep 17 00:00:00 2001 From: Martin Blumenstingl Date: Mon, 1 Apr 2019 19:57:48 +0200 Subject: pwm: meson: Use the spin-lock only to protect register modifications MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ Upstream commit f173747fffdf037c791405ab4f1ec0eb392fc48e ] 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 Reviewed-by: Uwe Kleine-König Reviewed-by: Neil Armstrong Signed-off-by: Thierry Reding Signed-off-by: Sasha Levin --- drivers/pwm/pwm-meson.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) (limited to 'drivers/pwm/pwm-meson.c') diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c index 9d5bd7d5c610..f58a4867b519 100644 --- a/drivers/pwm/pwm-meson.c +++ b/drivers/pwm/pwm-meson.c @@ -110,6 +110,10 @@ struct meson_pwm { const struct meson_pwm_data *data; void __iomem *base; u8 inverter_mask; + /* + * Protects register (write) access to the REG_MISC_AB register + * that is shared between the two PWMs. + */ spinlock_t lock; }; @@ -230,6 +234,7 @@ static void meson_pwm_enable(struct meson_pwm *meson, { u32 value, clk_shift, clk_enable, enable; unsigned int offset; + unsigned long flags; switch (id) { case 0: @@ -250,6 +255,8 @@ static void meson_pwm_enable(struct meson_pwm *meson, return; } + spin_lock_irqsave(&meson->lock, flags); + value = readl(meson->base + REG_MISC_AB); value &= ~(MISC_CLK_DIV_MASK << clk_shift); value |= channel->pre_div << clk_shift; @@ -262,11 +269,14 @@ static void meson_pwm_enable(struct meson_pwm *meson, value = readl(meson->base + REG_MISC_AB); value |= enable; writel(value, meson->base + REG_MISC_AB); + + spin_unlock_irqrestore(&meson->lock, flags); } static void meson_pwm_disable(struct meson_pwm *meson, unsigned int id) { u32 value, enable; + unsigned long flags; switch (id) { case 0: @@ -281,9 +291,13 @@ static void meson_pwm_disable(struct meson_pwm *meson, unsigned int id) return; } + spin_lock_irqsave(&meson->lock, flags); + value = readl(meson->base + REG_MISC_AB); value &= ~enable; writel(value, meson->base + REG_MISC_AB); + + spin_unlock_irqrestore(&meson->lock, flags); } static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, @@ -291,19 +305,16 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, { struct meson_pwm_channel *channel = pwm_get_chip_data(pwm); struct meson_pwm *meson = to_meson_pwm(chip); - unsigned long flags; int err = 0; if (!state) return -EINVAL; - spin_lock_irqsave(&meson->lock, flags); - if (!state->enabled) { meson_pwm_disable(meson, pwm->hwpwm); channel->state.enabled = false; - goto unlock; + return 0; } if (state->period != channel->state.period || @@ -324,7 +335,7 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, err = meson_pwm_calc(meson, channel, pwm->hwpwm, state->duty_cycle, state->period); if (err < 0) - goto unlock; + return err; channel->state.polarity = state->polarity; channel->state.period = state->period; @@ -336,9 +347,7 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, channel->state.enabled = true; } -unlock: - spin_unlock_irqrestore(&meson->lock, flags); - return err; + return 0; } static void meson_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm, -- cgit v1.2.3 From e5195f78632d2169529137b2891dfd5acc069dcf Mon Sep 17 00:00:00 2001 From: Bichao Zheng Date: Mon, 1 Apr 2019 20:18:17 +0200 Subject: pwm: meson: Don't disable PWM when setting duty repeatedly [ Upstream commit a279345807e1e0ae79567a52cfdd9d30c9174a3c ] There is an abnormally low about 20ms,when setting duty repeatedly. Because setting the duty will disable PWM and then enable. Delete this operation now. Fixes: 211ed630753d2f ("pwm: Add support for Meson PWM Controller") Signed-off-by: Bichao Zheng [ Dropped code instead of hiding it behind a comment ] Signed-off-by: Martin Blumenstingl Reviewed-by: Neil Armstrong Signed-off-by: Thierry Reding Signed-off-by: Sasha Levin --- drivers/pwm/pwm-meson.c | 5 ----- 1 file changed, 5 deletions(-) (limited to 'drivers/pwm/pwm-meson.c') diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c index f58a4867b519..a196439ee14c 100644 --- a/drivers/pwm/pwm-meson.c +++ b/drivers/pwm/pwm-meson.c @@ -320,11 +320,6 @@ static int meson_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, if (state->period != channel->state.period || state->duty_cycle != channel->state.duty_cycle || state->polarity != channel->state.polarity) { - if (channel->state.enabled) { - meson_pwm_disable(meson, pwm->hwpwm); - channel->state.enabled = false; - } - if (state->polarity != channel->state.polarity) { if (state->polarity == PWM_POLARITY_NORMAL) meson->inverter_mask |= BIT(pwm->hwpwm); -- cgit v1.2.3