linux-kernel - Re: [PATCH v2 1/3] pwm: Add pwm_cansleep() as exported API to users

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Date:	Mon, 28 Jan 2013 10:36:07 +0100
From:	Florian Vaussard <florian.vaussard@...l.ch>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
CC:	Thierry Reding <thierry.reding@...onic-design.de>,
	Bryan Wu <cooloney@...il.com>,
	Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] pwm: Add pwm_cansleep() as exported API to users

Hello,

Le 28/01/2013 09:45, Peter Ujfalusi a écrit :
> hi Thierry,
>
> On 01/26/2013 06:40 AM, Thierry Reding wrote:
>>> +  * @pwm: PWM device
>>> +  *
>>> +  * It returns nonzero if accessing the PWM can sleep.
>>> +  */
>>> +int pwm_cansleep(struct pwm_device *pwm)
>>
>> I actually liked pwm_can_sleep() better. I find it to be more consistent
>> with the naming of other function names. It would furthermore match the
>> field name.
>
> I was looking at the GPIO API to suggest this name change, but you are right
> we should be consistent with the PWM API here.
> Sorry Florian.
>

No problem, I agree with the PWM API consistency.

>>
>>> +{
>>> +	return pwm->chip->can_sleep;
>>> +}
>>> +EXPORT_SYMBOL_GPL(pwm_cansleep);
>>
>> Would it make sense to check for NULL pointers here? I guess that
>> passing NULL into the function could be considered a programming error
>> and an oops would be okay, but in that case there's no point in making
>> the function return an int. Also see my next comment.
>
> While it is unlikely to happen it is better to be safe, something like this
> will do:
>
> return pwm ? pwm->chip->can_sleep : 0;
>

Ok. And what about:

BUG_ON(pwm == NULL);
return pwm->chip->can_sleep;

>>
>>> +
>>>   #ifdef CONFIG_DEBUG_FS
>>>   static void pwm_dbg_show(struct pwm_chip *chip, struct seq_file *s)
>>>   {
>>> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
>>> index 70655a2..e2cb5c7 100644
>>> --- a/include/linux/pwm.h
>>> +++ b/include/linux/pwm.h
>>> @@ -146,6 +146,8 @@ struct pwm_ops {
>>>    * @base: number of first PWM controlled by this chip
>>>    * @npwm: number of PWMs controlled by this chip
>>>    * @pwms: array of PWM devices allocated by the framework
>>> + * @can_sleep: flag must be set iff config()/enable()/disable() methods sleep,
>>> + *      as they must while accessing PWM chips over I2C or SPI
>>>    */
>>>   struct pwm_chip {
>>>   	struct device		*dev;
>>> @@ -159,6 +161,7 @@ struct pwm_chip {
>>>   	struct pwm_device *	(*of_xlate)(struct pwm_chip *pc,
>>>   					    const struct of_phandle_args *args);
>>>   	unsigned int		of_pwm_n_cells;
>>> +	unsigned int		can_sleep:1;
>>
>> What's the reason for making this a bitfield? Couldn't we just use a
>> bool instead?
>
> I have also overlooked this. In my version I had the can_sleep as bool also.
>

Ok for a bool.

Thank you for your reviews. I will send a v3 sometimes today.

Cheers,
Florian
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