| Message ID | 20190401175748.5376-2-martin.blumenstingl@googlemail.com |
|---|---|
| State | New |
| Headers | show |
| Series | pwm: meson: fix scheduling while atomic issue | expand |
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>
On Mon, Apr 01, 2019 at 07:57:48PM +0200, 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(-) Applied, thanks. Thierry
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,
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(-)