linux-kernel - Re: [PATCH v2 3/3] pwm: core: add consumer device link

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Message-ID: <b9f1bb5c-36cd-f6e6-e6c6-a0257cf38b7e@st.com>
Date:   Tue, 12 Feb 2019 09:31:37 +0100
From:   Fabrice Gasnier <fabrice.gasnier@...com>
To:     Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
CC:     <thierry.reding@...il.com>, <robh+dt@...nel.org>,
        <tduszyns@...il.com>, <mark.rutland@....com>,
        <alexandre.torgue@...com>, <mcoquelin.stm32@...il.com>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-pwm@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH v2 3/3] pwm: core: add consumer device link

On 2/11/19 8:06 PM, Uwe Kleine-König wrote:
> Hello Fabrice,
> 
> On Mon, Feb 11, 2019 at 05:12:02PM +0100, Fabrice Gasnier wrote:
>> Add a device link between the PWM consumer and the PWM provider. This
>> enforces the PWM user to get suspended before the PWM provider. It
>> allows proper synchronization of suspend/resume sequences: the PWM user
>> is responsible for properly stopping PWM, before the provider gets
>> suspended: see [1]. Add the device link in:
>> - pwm_get()
>> - devm_pwm_get()
>> - devm_of_pwm_get()
>> as it requires a reference to the device for the PWM consumer.
>>
>> [1] https://lkml.org/lkml/2019/2/5/770
>>
>> Suggested-by: Thierry Reding <thierry.reding@...il.com>
>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
>> ---
>>  drivers/pwm/core.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>> index 1581f6a..2835e27 100644
>> --- a/drivers/pwm/core.c
>> +++ b/drivers/pwm/core.c
>> @@ -770,8 +770,13 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>>  	int err;
>>  
>>  	/* look up via DT first */
>> -	if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
>> -		return of_pwm_get(dev->of_node, con_id);
>> +	if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node) {
>> +		pwm = of_pwm_get(dev->of_node, con_id);
>> +		if (!IS_ERR(pwm))
>> +			device_link_add(dev, pwm->chip->dev,
>> +					DL_FLAG_AUTOREMOVE_CONSUMER);
>> +		return pwm;
>> +	}
>>  
>>  	/*
>>  	 * We look up the provider in the static table typically provided by
>> @@ -851,6 +856,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>>  	pwm->args.period = chosen->period;
>>  	pwm->args.polarity = chosen->polarity;
>>  
>> +	device_link_add(dev, pwm->chip->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
>> +
>>  	return pwm;
>>  }
>>  EXPORT_SYMBOL_GPL(pwm_get);
>> @@ -943,6 +950,8 @@ struct pwm_device *devm_of_pwm_get(struct device *dev, struct device_node *np,
>>  	if (!IS_ERR(pwm)) {
>>  		*ptr = pwm;
>>  		devres_add(dev, ptr);
>> +		device_link_add(dev, pwm->chip->dev,
>> +				DL_FLAG_AUTOREMOVE_CONSUMER);
> 
> IMHO it's surprising that devm_of_pwm_get() does more than of_pwm_get()
> + devres stuff. I'd put device_link_add() into of_pwm_get().

Hi Uwe,

I also agree with this. But I think this implies modifying the API for
of_pwm_get():
 /**
  * of_pwm_get() - request a PWM via the PWM framework
+ * @dev: device for PWM consumer
  * @np: device node to get the PWM from
  * @con_id: consumer name

It seems there aren't much of_pwm_get() users currently.
Does this look sensible ?

Best regards,
Fabrice

> 
> Best regards
> Uwe
>