Commit 68637b68 authored by Sangyun Kim's avatar Sangyun Kim Committed by Uwe Kleine-König
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pwm: atmel-tcb: Cache clock rates and mark chip as atomic 



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.

Acquire exclusive control over the clock rates with
clk_rate_exclusive_get() at probe time and cache the rates in struct
atmel_tcb_pwm_chip, then read the cached rates from
atmel_tcb_pwm_config(). This keeps the spinlock-based mutual exclusion
introduced in commit 37f77070 ("pwm: atmel-tcb: Fix race condition
and convert to guards") and removes the sleeping calls from the atomic
section.

With no sleeping calls left in .apply() and the regmap-mmio bus already
running with fast_io=true, also mark the chip as atomic so consumers
can use pwm_apply_atomic() from atomic context.

Fixes: 37f77070 ("pwm: atmel-tcb: Fix race condition and convert to guards")
Signed-off-by: default avatarSangyun Kim <sangyun.kim@snu.ac.kr>
Link: https://patch.msgid.link/20260419080838.3192357-1-sangyun.kim@snu.ac.kr


[ukleinek: Ensure .clk is enabled before calling clk_get_rate on it.]
Signed-off-by: default avatarUwe Kleine-König <ukleinek@kernel.org>
parent 5d087c48

drivers/pwm/pwm-atmel-tcb.c

+34 −4
Original line number Diff line number Diff line
@@ -50,6 +50,8 @@ struct atmel_tcb_pwm_chip { 
	spinlock_t lock;

	u8 channel;

	u8 width;

	unsigned long rate;

	unsigned long slow_rate;

	struct regmap *regmap;

	struct clk *clk;

	struct clk *gclk;
@@ -266,7 +268,7 @@ static int atmel_tcb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, 
	int slowclk = 0;

	unsigned period;

	unsigned duty;

	unsigned rate = clk_get_rate(tcbpwmc->clk);

	unsigned long rate = tcbpwmc->rate;

	unsigned long long min;

	unsigned long long max;
@@ -294,7 +296,7 @@ static int atmel_tcb_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm, 
	 */

	if (i == ARRAY_SIZE(atmel_tcb_divisors)) {

		i = slowclk;

		rate = clk_get_rate(tcbpwmc->slow_clk);

		rate = tcbpwmc->slow_rate;

		min = div_u64(NSEC_PER_SEC, rate);

		max = min << tcbpwmc->width;
@@ -431,24 +433,49 @@ static int atmel_tcb_pwm_probe(struct platform_device *pdev) 
	}



	chip->ops = &atmel_tcb_pwm_ops;

	chip->atomic = true;

	tcbpwmc->channel = channel;

	tcbpwmc->width = config->counter_width;



	err = clk_prepare_enable(tcbpwmc->slow_clk);

	err = clk_prepare_enable(tcbpwmc->clk);

	if (err)

		goto err_gclk;



	err = clk_prepare_enable(tcbpwmc->slow_clk);

	if (err)

		goto err_disable_clk;;



	err = clk_rate_exclusive_get(tcbpwmc->clk);

	if (err)

		goto err_disable_slow_clk;



	err = clk_rate_exclusive_get(tcbpwmc->slow_clk);

	if (err)

		goto err_clk_unlock;



	tcbpwmc->rate = clk_get_rate(tcbpwmc->clk);

	tcbpwmc->slow_rate = clk_get_rate(tcbpwmc->slow_clk);



	spin_lock_init(&tcbpwmc->lock);



	err = pwmchip_add(chip);

	if (err < 0)

		goto err_disable_clk;

		goto err_slow_clk_unlock;



	platform_set_drvdata(pdev, chip);



	return 0;



err_slow_clk_unlock:

	clk_rate_exclusive_put(tcbpwmc->slow_clk);



err_clk_unlock:

	clk_rate_exclusive_put(tcbpwmc->clk);



err_disable_clk:

	clk_disable_unprepare(tcbpwmc->clk);



err_disable_slow_clk:

	clk_disable_unprepare(tcbpwmc->slow_clk);



err_gclk:
@@ -470,6 +497,9 @@ static void atmel_tcb_pwm_remove(struct platform_device *pdev) 


	pwmchip_remove(chip);



	clk_rate_exclusive_put(tcbpwmc->slow_clk);

	clk_rate_exclusive_put(tcbpwmc->clk);

	clk_disable_unprepare(tcbpwmc->clk);

	clk_disable_unprepare(tcbpwmc->slow_clk);

	clk_put(tcbpwmc->gclk);

	clk_put(tcbpwmc->clk);