From: Martin Blumenstingl martin.blumenstingl@googlemail.com
[ 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 martin.blumenstingl@googlemail.com Reviewed-by: Uwe Kleine-König u.kleine-koenig@pengutronix.de Reviewed-by: Neil Armstrong narmstrong@baylibre.com Signed-off-by: Thierry Reding thierry.reding@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 c1ed641b3e266..f6e738ad7bd92 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,