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SubjectRe: [PATCH v3 3/3] pwm: core: add consumer device link
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On 2/13/19 4:17 PM, Fabrice Gasnier wrote:
> On 2/13/19 1:53 PM, Thierry Reding wrote:
>> On Wed, Feb 13, 2019 at 11:50:12AM +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_ 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 v3:
>>> - add struct device to of_get_pwm() arguments to handle device link from
>>> there.
>>> ---
>>> drivers/pwm/core.c | 14 +++++++++++---
>>> include/linux/pwm.h | 6 ++++--
>>> 2 files changed, 15 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>>> index 1581f6a..8cb5d4bc 100644
>>> --- a/drivers/pwm/core.c
>>> +++ b/drivers/pwm/core.c
>>> @@ -638,6 +638,7 @@ static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
>>>
>>> /**
>>> * 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
>>> *
>>> @@ -655,7 +656,8 @@ static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
>>> * Returns: A pointer to the requested PWM device or an ERR_PTR()-encoded
>>> * error code on failure.
>>> */
>>> -struct pwm_device *of_pwm_get(struct device_node *np, const char *con_id)
>>> +struct pwm_device *of_pwm_get(struct device *dev, struct device_node *np,
>>> + const char *con_id)
>>> {
>>> struct pwm_device *pwm = NULL;
>>> struct of_phandle_args args;
>>> @@ -689,6 +691,9 @@ struct pwm_device *of_pwm_get(struct device_node *np, const char *con_id)
>>> if (IS_ERR(pwm))
>>> goto put;
>>>
>>> + if (!device_link_add(dev, pwm->chip->dev, DL_FLAG_AUTOREMOVE_CONSUMER))
>>> + pr_debug("%s(): device link not added\n", __func__);
>>
>> I think it's better to turn this into dev_dbg(dev, ...) and maybe
>> mention which supplier it failed to link to, something like:
>>
>> if (!device_link_add(...))
>> dev_dbg(dev, "failed to create device link to %s\n",
>> pwm->chip->dev);
>
> Hi Thierry,
>
> Thanks for reviewing.
>
> I can update this: I used pr_debug() as there are pr_err() calls
> elsewhere in this routine.
> BTW, do you wish an additional patch to turn pr_err() into dev_err() in
> of_pwm_get()?
>
>>
>> Also, I wonder if this should perhaps be dev_err(). Under what
>> circumstances does this fail?
>
> Well, here is a comment from "device_link_add()" routine:
> "
> /*
> * If the supplier has not been fully registered yet or there is a
> * reverse dependency between the consumer and the supplier already in
> * the graph, return NULL.
> */
> "
>
> => Here the PWM supplier is already registered. (It seems a probe defer
> can be returned few lines above otherwise.)
>
> Other possibilities: kzalloc() failed, no consumer or supplier has been
> provided (or invalid flags, but this is hardcoded here.).
>
> So, I see two case here:
> 1 - The caller provided a 'dev' for PWM consumer... So, NULL link is an
> error when consumer & supplier has been passed correctly.
> => I can add a check on 'dev' for PWM consumer and report an error here:
> return -EINVAL
>
> 2 - The caller can't provide a 'dev' for PWM consumer as you mention
> bellow: "to allow code to get at the PWM if they didn't have..."
> => We should probably add a dev_warn() here, with no error ?
> Please see here after.
>
>>
>>> +
>>> /*
>>> * If a consumer name was not given, try to look it up from the
>>> * "pwm-names" property if it exists. Otherwise use the name of
>>> @@ -771,7 +776,7 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>>>
>>> /* look up via DT first */
>>> if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
>>> - return of_pwm_get(dev->of_node, con_id);
>>> + return of_pwm_get(dev, dev->of_node, con_id);
>>>
>>> /*
>>> * We look up the provider in the static table typically provided by
>>> @@ -851,6 +856,9 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>>> pwm->args.period = chosen->period;
>>> pwm->args.polarity = chosen->polarity;
>>>
>>> + if (!device_link_add(dev, pwm->chip->dev, DL_FLAG_AUTOREMOVE_CONSUMER))
>>> + pr_debug("%s(): device link not added\n", __func__);
>>
>> Same here. Also: not sure if we really need to include __func__ in the
>> message.
>>
>>> +
>>> return pwm;
>>> }
>>> EXPORT_SYMBOL_GPL(pwm_get);
>>> @@ -939,7 +947,7 @@ struct pwm_device *devm_of_pwm_get(struct device *dev, struct device_node *np,
>>> if (!ptr)
>>> return ERR_PTR(-ENOMEM);
>>>
>>> - pwm = of_pwm_get(np, con_id);
>>> + pwm = of_pwm_get(dev, np, con_id);
>>> if (!IS_ERR(pwm)) {
>>> *ptr = pwm;
>>> devres_add(dev, ptr);
>>> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
>>> index d5199b5..895e074 100644
>>> --- a/include/linux/pwm.h
>>> +++ b/include/linux/pwm.h
>>> @@ -406,7 +406,8 @@ struct pwm_device *of_pwm_xlate_with_flags(struct pwm_chip *pc,
>>> const struct of_phandle_args *args);
>>>
>>> struct pwm_device *pwm_get(struct device *dev, const char *con_id);
>>> -struct pwm_device *of_pwm_get(struct device_node *np, const char *con_id);
>>> +struct pwm_device *of_pwm_get(struct device *dev, struct device_node *np,
>>> + const char *con_id);
>>
>> I'm slightly concerned about this. I think one of the reasons why this
>> was introduced was to allow code to get at the PWM if they didn't have
>> a struct device * available. However, it doesn't seem like there are any
>> users of that function, so this seems fine.
>
> The git blame pointed out commit 8eb961279960:
> "
> pwm: core: Rename of_pwm_request() to of_pwm_get() and export it
>
> Allow client driver to use of_pwm_get() to get the PWM they need. This
> is needed for drivers which handle more than one PWM separately, like
> leds-pwm driver, which have:
> "
> ...
>
> For instance, I tested the leds-pwm driver. It uses the devm_* variant
> now (as others), there is a struct device * available. So yes, it seems
> fine.
>
> The only thing maybe out of tree code? This is where I have a doubt on
> having a mandatory struct device * to enforce consumer link creation...
> or make it optional (e.g. behave as a 'legacy' API) and warn the caller.
>
> Please let me know your feeling.

Hi Thierry,

I just sent a v4 to update the error handling following the cases
described above.

BR,
Fabrice
> Best regards,
> Fabrice
>
>>
>> Thierry
>>
>>> void pwm_put(struct pwm_device *pwm);
>>>
>>> struct pwm_device *devm_pwm_get(struct device *dev, const char *con_id);
>>> @@ -494,7 +495,8 @@ static inline struct pwm_device *pwm_get(struct device *dev,
>>> return ERR_PTR(-ENODEV);
>>> }
>>>
>>> -static inline struct pwm_device *of_pwm_get(struct device_node *np,
>>> +static inline struct pwm_device *of_pwm_get(struct device *dev,
>>> + struct device_node *np,
>>> const char *con_id)
>>> {
>>> return ERR_PTR(-ENODEV);
>>> --
>>> 1.9.1
>>>

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