[PATCH v11] pwm: bcm2835: Allow PWM driver to be used in atomic context

[PATCH v11] pwm: bcm2835: Allow PWM driver to be used in atomic context

[Sean Young]

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>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
---
 drivers/pwm/pwm-bcm2835.c | 38 +++++++++++++++++++++++++++++---------
 1 file changed, 29 insertions(+), 9 deletions(-)

diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c
index ab30667f4f95..307c0bd5f885 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 */
@@ -131,6 +126,13 @@ static const struct pwm_ops bcm2835_pwm_ops = {
 	.apply = bcm2835_pwm_apply,
 };
 
+static void devm_clk_rate_exclusive_put(void *data)
+{
+	struct clk *clk = data;
+
+	clk_rate_exclusive_put(clk);
+}
+
 static int bcm2835_pwm_probe(struct platform_device *pdev)
 {
 	struct bcm2835_pwm *pc;
@@ -151,8 +153,26 @@ 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");
+
+	ret = devm_add_action_or_reset(&pdev->dev, devm_clk_rate_exclusive_put,
+				       pc->clk);
+	if (ret) {
+		clk_rate_exclusive_put(pc->clk);
+		return ret;
+	}
+
+	pc->rate = clk_get_rate(pc->clk);
+	if (!pc->rate)
+		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;
 
 	platform_set_drvdata(pdev, pc);
-- 
2.43.0

Re: [PATCH v11] pwm: bcm2835: Allow PWM driver to be used in atomic context

[Thierry Reding]

On Wed, 20 Dec 2023 14:24:25 +0000, Sean Young wrote:
> clk_get_rate() may do a mutex lock. Fetch the clock rate once, and prevent
> rate changes using clk_rate_exclusive_get().
> 
> 

Applied, thanks!

[1/1] pwm: bcm2835: Allow PWM driver to be used in atomic context
      commit: fcc76072935935082efa127b97c7ddd880d2d793

Best regards,
-- 
Thierry Reding <thierry.reding@gmail.com>

Re: [PATCH v11] pwm: bcm2835: Allow PWM driver to be used in atomic context

[Uwe Kleine-König]

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Hello Sean,

On Wed, Dec 20, 2023 at 02:24:25PM +0000, Sean Young wrote:
> @@ -151,8 +153,26 @@ 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");
> +
> +	ret = devm_add_action_or_reset(&pdev->dev, devm_clk_rate_exclusive_put,
> +				       pc->clk);
> +	if (ret) {
> +		clk_rate_exclusive_put(pc->clk);

That clk_rate_exclusive_put() is wrong. If devm_add_action_or_reset()
fails that is already cared for.

Given that Thierry already applied this patch, getting this fixed in a
timely manner would be good.

> +		return ret;
> +	}
> +
> +	pc->rate = clk_get_rate(pc->clk);
> +	if (!pc->rate)
> +		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;
>  
>  	platform_set_drvdata(pdev, pc);

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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Re: [PATCH v11] pwm: bcm2835: Allow PWM driver to be used in atomic context

[Sean Young]

On Fri, Dec 22, 2023 at 11:30:47AM +0100, Uwe Kleine-König wrote:
> Hello Sean,
> 
> On Wed, Dec 20, 2023 at 02:24:25PM +0000, Sean Young wrote:
> > @@ -151,8 +153,26 @@ 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");
> > +
> > +	ret = devm_add_action_or_reset(&pdev->dev, devm_clk_rate_exclusive_put,
> > +				       pc->clk);
> > +	if (ret) {
> > +		clk_rate_exclusive_put(pc->clk);
> 
> That clk_rate_exclusive_put() is wrong. If devm_add_action_or_reset()
> fails that is already cared for.

Yes, you're right. I missed that - should've checked.

> Given that Thierry already applied this patch, getting this fixed in a
> timely manner would be good.

I'll send out a patch shortly, thanks for catching.


Sean