Messages in this thread | | | Subject | Re: [PATCH v2 1/1] pwm: meson: use the spin-lock only to protect register modifications | From | Neil Armstrong <> | Date | Wed, 3 Apr 2019 13:21:24 +0200 |
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On 01/04/2019 19:57, Martin Blumenstingl wrote: > 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.blumenstingl@googlemail.com> > Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> > --- > drivers/pwm/pwm-meson.c | 25 +++++++++++++++++-------- > 1 file changed, 17 insertions(+), 8 deletions(-) > > diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c > index c1ed641b3e26..f6e738ad7bd9 100644 > --- a/drivers/pwm/pwm-meson.c > +++ b/drivers/pwm/pwm-meson.c > @@ -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 || > @@ -329,7 +340,7 @@ 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 +352,7 @@ 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, >
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
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