Commit f173747f authored by Martin Blumenstingl's avatar Martin Blumenstingl Committed by Thierry Reding
Browse files

pwm: meson: Use the spin-lock only to protect register modifications 



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: 211ed630 ("pwm: Add support for Meson PWM Controller")
Signed-off-by: default avatarMartin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: default avatarNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent a2793458

drivers/pwm/pwm-meson.c

+17 −8
Original line number Diff line number Diff line
@@ -111,6 +111,10 @@ 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;

};
@@ -235,6 +239,7 @@ 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:
@@ -255,6 +260,8 @@ 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;
@@ -267,11 +274,14 @@ 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:
@@ -286,9 +296,13 @@ 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,
@@ -296,19 +310,16 @@ 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,

CRA Git | Maintained and supported by SUSTech CRA and CCSE