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Subject: Re: [PATCH v4 3/3] pwm: core: add consumer device link
To:     =?UTF-8?Q?Uwe_Kleine-K=c3=b6nig?= <u.kleine-koenig@pengutronix.de>
CC:     <thierry.reding@gmail.com>, <robh+dt@kernel.org>,
        <tduszyns@gmail.com>, <mark.rutland@arm.com>,
        <alexandre.torgue@st.com>, <mcoquelin.stm32@gmail.com>,
        <devicetree@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-pwm@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>
References: <1550139951-25788-1-git-send-email-fabrice.gasnier@st.com>
 <1550139951-25788-4-git-send-email-fabrice.gasnier@st.com>
 <20190218172223.lw3e5tn5hzsow6tg@pengutronix.de>
From:   Fabrice Gasnier <fabrice.gasnier@st.com>
Message-ID: <53bc3d80-8732-46be-caef-015998c9ad0e@st.com>
Date:   Tue, 19 Feb 2019 09:46:32 +0100
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On 2/18/19 6:22 PM, Uwe Kleine-König wrote:
> Hello,
> 
> On Thu, Feb 14, 2019 at 11:25:51AM +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:
>> - of_pwm_get()
>> - pwm_get()
>> - devm_*pwm_get() variants
>> 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@gmail.com>
>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
>> ---
>> Changes in v4:
>> - rework error handling following Thierry's comments
>> - turn/split pr_debug() into dev_err()/pr_warn().
>>
>> Changes in v3:
>> - add struct device to of_get_pwm() arguments to handle device link from
>>   there as discussed with Uwe.
>> ---
>>  drivers/pwm/core.c  | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
>>  include/linux/pwm.h |  6 ++++--
>>  2 files changed, 51 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>> index 1581f6a..64e10a6 100644
>> --- a/drivers/pwm/core.c
>> +++ b/drivers/pwm/core.c
>> @@ -636,8 +636,35 @@ static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
>>  	return ERR_PTR(-EPROBE_DEFER);
>>  }
>>  
>> +static struct device_link *pwm_device_link_add(struct device *dev,
>> +					       struct pwm_device *pwm)
>> +{
>> +	struct device_link *dl;
>> +
>> +	if (!dev) {
>> +		/*
>> +		 * No device for the PWM consumer has been provided. It may
>> +		 * impact the PM sequence ordering: the PWM supplier may get
>> +		 * suspended before the consumer.
>> +		 */
>> +		pr_warn("no consumer dev, can't create device link to %s\n",
>> +			dev_name(pwm->chip->dev));
> 
> Maybe use dev_warn(pwm->chip->dev, ...) ?

Hi Uwe,

I'm wondering a bit about this: In this case, the caller that doesn't
provide a struct device *, PWM provider isn't responsible for that. So I
just hope this wouldn't be miss-leading ?

> 
>> +		return NULL;
>> +	}
>> +
>> +	dl = device_link_add(dev, pwm->chip->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
>> +	if (!dl) {
>> +		dev_err(dev, "failed to create device link to %s\n",
>> +			dev_name(pwm->chip->dev));
>> +			return ERR_PTR(-EINVAL);
> 
> broken indention.

Oops, I'll fix it.

Thanks,
Fabrice

> 
>> +	}
>> +
>> +	return dl;
>> +}
>> +
> 
> Best regards
> Uwe
>