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 <martin.blumensti...@googlemail.com> --- drivers/pwm/pwm-meson.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c index c1ed641b3e26..2b03938039b6 100644 --- a/drivers/pwm/pwm-meson.c +++ b/drivers/pwm/pwm-meson.c @@ -235,6 +235,7 @@ 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 +256,8 @@ 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 +270,14 @@ 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 +292,13 @@ 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 +306,16 @@ 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 || @@ -329,7 +336,7 @@ 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; @@ -341,9 +348,7 @@ 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, -- 2.21.0