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[PATCH] Input: pwm-beeper - defer pwm config if pwm can sleep

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  [PATCH] Input: pwm-beeper - defer pwm config if pwm can sleep Manfred Schlaegl <manfred.schlaegl@gmx.at> - 2016-02-17 14:20 +0100
    Re: [PATCH] Input: pwm-beeper - defer pwm config if pwm can sleep Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-02-22 20:50 +0100
      Re: [PATCH] Input: pwm-beeper - defer pwm config if pwm can sleep Manfred Schlaegl <manfred.schlaegl@gmx.at> - 2016-02-23 09:50 +0100

#1336413 — [PATCH] Input: pwm-beeper - defer pwm config if pwm can sleep

If the pwm can sleep defer actions to it using a worker.
A similar approach was used in leds-pwm (c971ff185)

Trigger:
On a Freescale i.MX53 based board we ran into "BUG: scheduling while
atomic" because input_inject_event locks interrupts, but
imx_pwm_config_v2 sleeps.

Tested on Freescale i.MX53 SoC with 4.5-rc1 and 4.1.

Unmodified applicable to
 * 4.5-rc4
 * 4.4.1 (stable)
 * 4.3.5 (stable)
 * 4.1.18 (longterm)

Modified applicable to
 * 3.18.27 (longterm)

Signed-off-by: Manfred Schlaegl <manfred.schlaegl@gmx.at>
---
 drivers/input/misc/pwm-beeper.c | 62 +++++++++++++++++++++++++++++------------
 1 file changed, 44 insertions(+), 18 deletions(-)

diff --git a/drivers/input/misc/pwm-beeper.c b/drivers/input/misc/pwm-beeper.c
index f2261ab..c160b5e 100644
--- a/drivers/input/misc/pwm-beeper.c
+++ b/drivers/input/misc/pwm-beeper.c
@@ -20,21 +20,42 @@
 #include <linux/platform_device.h>
 #include <linux/pwm.h>
 #include <linux/slab.h>
+#include <linux/workqueue.h>
 
 struct pwm_beeper {
 	struct input_dev *input;
 	struct pwm_device *pwm;
+	struct work_struct work;
 	unsigned long period;
+	bool can_sleep;
 };
 
 #define HZ_TO_NANOSECONDS(x) (1000000000UL/(x))
 
+static void __pwm_beeper_set(struct pwm_beeper *beeper)
+{
+	unsigned long period = beeper->period;
+
+	pwm_config(beeper->pwm, period / 2, period);
+
+	if (period == 0)
+		pwm_disable(beeper->pwm);
+	else
+		pwm_enable(beeper->pwm);
+}
+
+static void pwm_beeper_work(struct work_struct *work)
+{
+	struct pwm_beeper *beeper =
+		container_of(work, struct pwm_beeper, work);
+
+	__pwm_beeper_set(beeper);
+}
+
 static int pwm_beeper_event(struct input_dev *input,
 			    unsigned int type, unsigned int code, int value)
 {
-	int ret = 0;
 	struct pwm_beeper *beeper = input_get_drvdata(input);
-	unsigned long period;
 
 	if (type != EV_SND || value < 0)
 		return -EINVAL;
@@ -49,18 +70,15 @@ static int pwm_beeper_event(struct input_dev *input,
 		return -EINVAL;
 	}
 
-	if (value == 0) {
-		pwm_disable(beeper->pwm);
-	} else {
-		period = HZ_TO_NANOSECONDS(value);
-		ret = pwm_config(beeper->pwm, period / 2, period);
-		if (ret)
-			return ret;
-		ret = pwm_enable(beeper->pwm);
-		if (ret)
-			return ret;
-		beeper->period = period;
-	}
+	if (value == 0)
+		beeper->period = 0;
+	else
+		beeper->period = HZ_TO_NANOSECONDS(value);
+
+	if (beeper->can_sleep)
+		schedule_work(&beeper->work);
+	else
+		__pwm_beeper_set(beeper);
 
 	return 0;
 }
@@ -87,6 +105,10 @@ static int pwm_beeper_probe(struct platform_device *pdev)
 		goto err_free;
 	}
 
+	beeper->can_sleep = pwm_can_sleep(beeper->pwm);
+	if (beeper->can_sleep)
+		INIT_WORK(&beeper->work, pwm_beeper_work);
+
 	beeper->input = input_allocate_device();
 	if (!beeper->input) {
 		dev_err(&pdev->dev, "Failed to allocate input device\n");
@@ -133,6 +155,9 @@ static int pwm_beeper_remove(struct platform_device *pdev)
 {
 	struct pwm_beeper *beeper = platform_get_drvdata(pdev);
 
+	if (beeper->can_sleep)
+		cancel_work_sync(&beeper->work);
+
 	input_unregister_device(beeper->input);
 
 	pwm_disable(beeper->pwm);
@@ -147,6 +172,9 @@ static int __maybe_unused pwm_beeper_suspend(struct device *dev)
 {
 	struct pwm_beeper *beeper = dev_get_drvdata(dev);
 
+	if (beeper->can_sleep)
+		cancel_work_sync(&beeper->work);
+
 	if (beeper->period)
 		pwm_disable(beeper->pwm);
 
@@ -157,10 +185,8 @@ static int __maybe_unused pwm_beeper_resume(struct device *dev)
 {
 	struct pwm_beeper *beeper = dev_get_drvdata(dev);
 
-	if (beeper->period) {
-		pwm_config(beeper->pwm, beeper->period / 2, beeper->period);
-		pwm_enable(beeper->pwm);
-	}
+	if (beeper->period)
+		__pwm_beeper_set(beeper);
 
 	return 0;
 }
-- 
2.1.4

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#1339871

On Wed, Feb 17, 2016 at 02:19:26PM +0100, Manfred Schlaegl wrote:
> If the pwm can sleep defer actions to it using a worker.
> A similar approach was used in leds-pwm (c971ff185)
> 
> Trigger:
> On a Freescale i.MX53 based board we ran into "BUG: scheduling while
> atomic" because input_inject_event locks interrupts, but
> imx_pwm_config_v2 sleeps.
> 
> Tested on Freescale i.MX53 SoC with 4.5-rc1 and 4.1.
> 
> Unmodified applicable to
>  * 4.5-rc4
>  * 4.4.1 (stable)
>  * 4.3.5 (stable)
>  * 4.1.18 (longterm)
> 
> Modified applicable to
>  * 3.18.27 (longterm)
> 
> Signed-off-by: Manfred Schlaegl <manfred.schlaegl@gmx.at>
> ---
>  drivers/input/misc/pwm-beeper.c | 62 +++++++++++++++++++++++++++++------------
>  1 file changed, 44 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/input/misc/pwm-beeper.c b/drivers/input/misc/pwm-beeper.c
> index f2261ab..c160b5e 100644
> --- a/drivers/input/misc/pwm-beeper.c
> +++ b/drivers/input/misc/pwm-beeper.c
> @@ -20,21 +20,42 @@
>  #include <linux/platform_device.h>
>  #include <linux/pwm.h>
>  #include <linux/slab.h>
> +#include <linux/workqueue.h>
>  
>  struct pwm_beeper {
>  	struct input_dev *input;
>  	struct pwm_device *pwm;
> +	struct work_struct work;
>  	unsigned long period;
> +	bool can_sleep;

I wonder if it is not better to always schedule work, regardless of
whether PWM may sleep or not.

Thanks.

-- 
Dmitry

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#1340404

On 2016-02-22 20:46, Dmitry Torokhov wrote:
> On Wed, Feb 17, 2016 at 02:19:26PM +0100, Manfred Schlaegl wrote:
>> If the pwm can sleep defer actions to it using a worker.
>> A similar approach was used in leds-pwm (c971ff185)
>>
>> Trigger:
>> On a Freescale i.MX53 based board we ran into "BUG: scheduling while
>> atomic" because input_inject_event locks interrupts, but
>> imx_pwm_config_v2 sleeps.
>>
>> Tested on Freescale i.MX53 SoC with 4.5-rc1 and 4.1.
>>
>> Unmodified applicable to
>>  * 4.5-rc4
>>  * 4.4.1 (stable)
>>  * 4.3.5 (stable)
>>  * 4.1.18 (longterm)
>>
>> Modified applicable to
>>  * 3.18.27 (longterm)
>>
>> Signed-off-by: Manfred Schlaegl <manfred.schlaegl@gmx.at>
>> ---
>>  drivers/input/misc/pwm-beeper.c | 62 +++++++++++++++++++++++++++++------------
>>  1 file changed, 44 insertions(+), 18 deletions(-)
>>
>> diff --git a/drivers/input/misc/pwm-beeper.c b/drivers/input/misc/pwm-beeper.c
>> index f2261ab..c160b5e 100644
>> --- a/drivers/input/misc/pwm-beeper.c
>> +++ b/drivers/input/misc/pwm-beeper.c
>> @@ -20,21 +20,42 @@
>>  #include <linux/platform_device.h>
>>  #include <linux/pwm.h>
>>  #include <linux/slab.h>
>> +#include <linux/workqueue.h>
>>  
>>  struct pwm_beeper {
>>  	struct input_dev *input;
>>  	struct pwm_device *pwm;
>> +	struct work_struct work;
>>  	unsigned long period;
>> +	bool can_sleep;
> 
> I wonder if it is not better to always schedule work, regardless of
> whether PWM may sleep or not.
> 
> Thanks.
> 

In my opinion there is no real strong argument to do it this or that way.
I decided to do it this way because of following weaker arguments:
 1. If pwm can not sleep the behavior stays exactly the same as before
 2. The introduced conditions do not really add much complexity to the code
 3. It was successfully done the same way in leds-pwm

Best regards,
Manfred

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