[PATCH] pwm: atmel-tcb: Fix sleeping function called from invalid context

[Sangyun Kim]

atmel_tcb_pwm_apply() holds tcbpwmc->lock as a spinlock via
guard(spinlock)() and then calls atmel_tcb_pwm_config(), which calls
clk_get_rate() twice. clk_get_rate() acquires clk_prepare_lock (a
mutex), so this is a sleep-in-atomic-context violation.

On CONFIG_DEBUG_ATOMIC_SLEEP kernels every pwm_apply_state() that
enables or reconfigures the PWM triggers a "BUG: sleeping function
called from invalid context" warning.

All callers of tcbpwmc->lock (the .request and .apply callbacks) run in
process context and only need mutual exclusion against each other, so
use a mutex instead of a spinlock and allow the sleeping calls inside
atmel_tcb_pwm_config().

Fixes: 37f7707077f5 ("pwm: atmel-tcb: Fix race condition and convert to guards")
Signed-off-by: Sangyun Kim <sangyun.kim@xxxxxxxxx>
---
 drivers/pwm/pwm-atmel-tcb.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/pwm/pwm-atmel-tcb.c b/drivers/pwm/pwm-atmel-tcb.c
index f9ff78ba122d..6405e82d9f10 100644
--- a/drivers/pwm/pwm-atmel-tcb.c
+++ b/drivers/pwm/pwm-atmel-tcb.c
@@ -17,6 +17,7 @@
 #include <linux/ioport.h>
 #include <linux/io.h>
 #include <linux/mfd/syscon.h>
+#include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/pwm.h>
 #include <linux/of.h>
@@ -47,7 +48,7 @@ struct atmel_tcb_channel {
 };
 
 struct atmel_tcb_pwm_chip {
-	spinlock_t lock;
+	struct mutex lock;
 	u8 channel;
 	u8 width;
 	struct regmap *regmap;
@@ -81,7 +82,7 @@ static int atmel_tcb_pwm_request(struct pwm_chip *chip,
 	tcbpwm->period = 0;
 	tcbpwm->div = 0;
 
-	guard(spinlock)(&tcbpwmc->lock);
+	guard(mutex)(&tcbpwmc->lock);
 
 	regmap_read(tcbpwmc->regmap, ATMEL_TC_REG(tcbpwmc->channel, CMR), &cmr);
 	/*
@@ -335,7 +336,7 @@ static int atmel_tcb_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	int duty_cycle, period;
 	int ret;
 
-	guard(spinlock)(&tcbpwmc->lock);
+	guard(mutex)(&tcbpwmc->lock);
 
 	if (!state->enabled) {
 		atmel_tcb_pwm_disable(chip, pwm, state->polarity);
@@ -438,7 +439,7 @@ static int atmel_tcb_pwm_probe(struct platform_device *pdev)
 	if (err)
 		goto err_gclk;
 
-	spin_lock_init(&tcbpwmc->lock);
+	mutex_init(&tcbpwmc->lock);
 
 	err = pwmchip_add(chip);
 	if (err < 0)
-- 
2.34.1