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pwm: atmel-tcb: Cache clock rates and mark chip as atomic

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[ Upstream commit 68637b68af ]

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 37f7707077 ("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: 37f7707077 ("pwm: atmel-tcb: Fix race condition and convert to guards")
Signed-off-by: Sangyun 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: Uwe Kleine-König <ukleinek@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Sangyun Kim
2026-04-19 17:08:38 +09:00
committed by Greg Kroah-Hartman
parent de62cefa31
commit dd60f26fd8
1 changed files with 34 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files
drivers/pwm/pwm-atmel-tcb.c
+34 -4
View File
@@ -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);