[PATCH v6 3/4] pwm: bcm2835: allow pwm driver to be used in atomic context

Sean Young
2023-11-29T09:14:16Z

clk_get_rate() may do a mutex lock. Fetch the clock rate once, and prevent
rate changes using clk_rate_exclusive_get().

Signed-off-by: Sean Young <sean@mess.org>
---
drivers/pwm/pwm-bcm2835.c | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c
index 9777babd5b95..52748194a3da 100644
--- a/drivers/pwm/pwm-bcm2835.c
+++ b/drivers/pwm/pwm-bcm2835.c
@@ -28,6 +28,7 @@ struct bcm2835_pwm {
struct device *dev;
void __iomem *base;
struct clk *clk;
+ unsigned long rate;
};

static inline struct bcm2835_pwm *to_bcm2835_pwm(struct pwm_chip *chip)
@@ -63,17 +64,11 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
{

struct bcm2835_pwm *pc = to_bcm2835_pwm(chip);
- unsigned long rate = clk_get_rate(pc->clk);
unsigned long long period_cycles;
u64 max_period;

u32 val;

- if (!rate) {
- dev_err(pc->dev, "failed to get clock rate\n");
- return -EINVAL;
- }
-
/*
* period_cycles must be a 32 bit value, so period * rate / NSEC_PER_SEC
* must be <= U32_MAX. As U32_MAX * NSEC_PER_SEC < U64_MAX the
@@ -88,13 +83,13 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
* <=> period < ((U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC/2) / rate
* <=> period <= ceil((U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC/2) / rate) - 1
*/
- max_period = DIV_ROUND_UP_ULL((u64)U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC / 2, rate) - 1;
+ max_period = DIV_ROUND_UP_ULL((u64)U32_MAX * NSEC_PER_SEC + NSEC_PER_SEC / 2, pc->rate) - 1;

if (state->period > max_period)
return -EINVAL;

/* set period */
- period_cycles = DIV_ROUND_CLOSEST_ULL(state->period * rate, NSEC_PER_SEC);
+ period_cycles = DIV_ROUND_CLOSEST_ULL(state->period * pc->rate, NSEC_PER_SEC);

/* don't accept a period that is too small */
if (period_cycles < PERIOD_MIN)
@@ -103,7 +98,7 @@ static int bcm2835_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
writel(period_cycles, pc->base + PERIOD(pwm->hwpwm));

/* set duty cycle */
- val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * rate, NSEC_PER_SEC);
+ val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * pc->rate, NSEC_PER_SEC);
writel(val, pc->base + DUTY(pwm->hwpwm));

/* set polarity */
@@ -151,14 +146,29 @@ static int bcm2835_pwm_probe(struct platform_device *pdev)
return dev_err_probe(&pdev->dev, PTR_ERR(pc->clk),
"clock not found\n");

+ ret = clk_rate_exclusive_get(pc->clk);
+ if (ret)
+ return dev_err_probe(&pdev->dev, ret,
+ "fail to get exclusive rate\n");
+
+ pc->rate = clk_get_rate(pc->clk);
+ if (!pc->rate) {
+ clk_rate_exclusive_put(pc->clk);
+ return dev_err_probe(&pdev->dev, -EINVAL,
+ "failed to get clock rate\n");
+ }
+
pc->chip.dev = &pdev->dev;
pc->chip.ops = &bcm2835_pwm_ops;
+ pc->chip.atomic = true;
pc->chip.npwm = 2;

ret = devm_pwmchip_add(&pdev->dev, &pc->chip);
- if (ret < 0)
+ if (ret < 0) {
+ clk_rate_exclusive_put(pc->clk);
return dev_err_probe(&pdev->dev, ret,
"failed to add pwmchip\n");
+ }

return 0;
}
@@ -167,6 +177,7 @@ static int bcm2835_pwm_suspend(struct device *dev)
{
struct bcm2835_pwm *pc = dev_get_drvdata(dev);

+ clk_rate_exclusive_put(pc->clk);
clk_disable_unprepare(pc->clk);

return 0;
--
2.43.0