From: Martin Blumenstingl <martin.blumensti...@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.blumensti...@googlemail.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koe...@pengutronix.de>
Reviewed-by: Neil Armstrong <narmstr...@baylibre.com>
Signed-off-by: Thierry Reding <thierry.red...@gmail.com>
Signed-off-by: Sasha Levin <sas...@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 9d5bd7d5c610b..f58a4867b5194 100644
--- a/drivers/pwm/pwm-meson.c
+++ b/drivers/pwm/pwm-meson.c
@@ -110,6 +110,10 @@ 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;
};
@@ -230,6 +234,7 @@ 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:
@@ -250,6 +255,8 @@ 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;
@@ -262,11 +269,14 @@ 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:
@@ -281,9 +291,13 @@ 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,
@@ -291,19 +305,16 @@ 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,
--
2.20.1
