diff mbox series

[v8,5/6] pwm: bcm2835: Allow PWM driver to be used in atomic context

Message ID e9e32c9789da3c90b5a2aa7d5a093120b76421fb.1702369869.git.sean@mess.org (mailing list archive)
State New, archived
Headers show
Series Improve pwm-ir-tx precision | expand

Commit Message

Sean Young Dec. 12, 2023, 8:34 a.m. UTC 
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 | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

Comments

Uwe Kleine-König Dec. 12, 2023, 11:50 a.m. UTC | #1 
On Tue, Dec 12, 2023 at 08:34:04AM +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().
> 
> Signed-off-by: Sean Young <sean@mess.org>
> Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>

Looks good,

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

Best regards
Uwe
Uwe Kleine-König Dec. 12, 2023, 4:08 p.m. UTC | #2 
Hello Sean,

On Tue, Dec 12, 2023 at 08:34:04AM +0000, Sean Young wrote:
> @@ -169,6 +179,7 @@ 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);

I thought this was the remove function, but that's suspend. Adding
clk_rate_exclusive_put() there is wrong.

Best regards
Uwe
Florian Fainelli Dec. 12, 2023, 4:11 p.m. UTC | #3 
On 12/12/2023 8:08 AM, Uwe Kleine-König wrote:
> Hello Sean,
> 
> On Tue, Dec 12, 2023 at 08:34:04AM +0000, Sean Young wrote:
>> @@ -169,6 +179,7 @@ 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);
> 
> I thought this was the remove function, but that's suspend. Adding
> clk_rate_exclusive_put() there is wrong.

Oh yes I missed that somehow, good catch Uwe!
Uwe Kleine-König Dec. 12, 2023, 6:14 p.m. UTC | #4 
Hello Sean,

On Tue, Dec 12, 2023 at 05:08:38PM +0100, Uwe Kleine-König wrote:
> On Tue, Dec 12, 2023 at 08:34:04AM +0000, Sean Young wrote:
> > @@ -169,6 +179,7 @@ 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);
> 
> I thought this was the remove function, but that's suspend. Adding
> clk_rate_exclusive_put() there is wrong.

https://lore.kernel.org/linux-clk/744a6371f94fe96f527eea6e52a600914e6fb6b5.1702403904.git.u.kleine-koenig@pengutronix.de/
might be useful to fix this.

Best regards
Uwe
Sean Young Dec. 18, 2023, 9:02 a.m. UTC | #5 
On Tue, Dec 12, 2023 at 07:14:44PM +0100, Uwe Kleine-König wrote:
> Hello Sean,
> 
> On Tue, Dec 12, 2023 at 05:08:38PM +0100, Uwe Kleine-König wrote:
> > On Tue, Dec 12, 2023 at 08:34:04AM +0000, Sean Young wrote:
> > > @@ -169,6 +179,7 @@ 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);
> > 
> > I thought this was the remove function, but that's suspend. Adding
> > clk_rate_exclusive_put() there is wrong.
> 
> https://lore.kernel.org/linux-clk/744a6371f94fe96f527eea6e52a600914e6fb6b5.1702403904.git.u.kleine-koenig@pengutronix.de/
> might be useful to fix this.

That does look useful, I suppose I can only use it once it's merged in
pwm-next though. Leaving out for v9.

Thanks,
Sean
Sean Young Dec. 18, 2023, 9:02 a.m. UTC | #6 
On Tue, Dec 12, 2023 at 05:08:38PM +0100, Uwe Kleine-König wrote:
> Hello Sean,
> 
> On Tue, Dec 12, 2023 at 08:34:04AM +0000, Sean Young wrote:
> > @@ -169,6 +179,7 @@ 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);
> 
> I thought this was the remove function, but that's suspend. Adding
> clk_rate_exclusive_put() there is wrong.

Nice catch - fixed in v9.


Sean
diff mbox series

Patch

diff --git a/drivers/pwm/pwm-bcm2835.c b/drivers/pwm/pwm-bcm2835.c
index ab30667f4f951..309d52ec43bbe 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 */
@@ -151,16 +146,31 @@  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;
 
 	platform_set_drvdata(pdev, pc);
 
 	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;
 }
@@ -169,6 +179,7 @@  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;