Message-id: <58DB8377.3030507@samsung.com>
Date:   Wed, 29 Mar 2017 18:50:47 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] extcon: Allow registering a single notifier for all
 cables on an extcon_dev

Hi,

On 2017년 03월 29일 16:38, Hans de Goede wrote:
> Hi,
> 
> On 29-03-17 09:06, Chanwoo Choi wrote:
>> Hi,
>>
>> On 2017년 03월 25일 23:03, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 20-03-17 10:48, Hans de Goede wrote:
>>>> Hi,
>>>>
>>>> On 20-03-17 01:55, Chanwoo Choi wrote:
>>>>> Hi,
>>>>>
>>>>> On 2017년 03월 20일 03:23, Hans de Goede wrote:
>>>>>> In some cases a driver may want to monitor multiple cables on a single
>>>>>> extcon. For example a charger driver will typically want to monitor all
>>>>>> of EXTCON_CHG_USB_SDP, EXTCON_CHG_USB_CDP, EXTCON_CHG_USB_DCP to configure
>>>>>> the max. current it can sink while charging.
>>>>>>
>>>>>> Due to the signature of the notifier_call function + how extcon passes
>>>>>> state and the extcon_dev as parameters this requires using one
>>>>>> notifier_block + one notifier_call function per cable, otherwise the
>>>>>> notifier_call function cannot get to its driver's data (using container_of
>>>>>> requires it to know which notifier block its first parameter is).
>>>>>>
>>>>>> For a driver wanting to monitor the above 3 cables that would result
>>>>>> in something like this:
>>>>>>
>>>>>> static const unsigned int vbus_cable_ids[] = {
>>>>>>     EXTCON_CHG_USB_SDP, EXTCON_CHG_USB_CDP, EXTCON_CHG_USB_DCP };
>>>>>>
>>>>>> struct driver_data {
>>>>>>     struct notifier_block vbus_nb[ARRAY_SIZE(vbus_cable_ids)];
>>>>>> }
>>>>>>
>>>>>> /*
>>>>>>  * We need 3 copies of this, because there is no way to find out for which
>>>>>>  * cable id we are being called from the passed in arguments; and we must
>>>>>>  * have a separate nb for each extcon_register_notifier call.
>>>>>>  */
>>>>>> static int vbus_cable0_evt(struct notifier_block *nb, unsigned long e, void *p)
>>>>>> {
>>>>>>     struct driver_data *data =
>>>>>>         container_of(nb, struct driver_data, vbus_nb[0]);
>>>>>>     ...
>>>>>> }
>>>>>>
>>>>>> static int vbus_cable1_evt(struct notifier_block *nb, unsigned long e, void *p)
>>>>>> {
>>>>>>     struct driver_data *data =
>>>>>>         container_of(nb, struct driver_data, vbus_nb[1]);
>>>>>>     ...
>>>>>> }
>>>>>>
>>>>>> static int vbus_cable2_evt(struct notifier_block *nb, unsigned long e, void *p)
>>>>>> {
>>>>>>     struct driver_data *data =
>>>>>>         container_of(nb, struct driver_data, vbus_nb[2]);
>>>>>>     ...
>>>>>> }
>>>>>>
>>>>>> int probe(...)
>>>>>> {
>>>>>>     /* Register for vbus notification */
>>>>>>     data->vbus_nb[0].notifier_call = vbus_cable0_evt;
>>>>>>     data->vbus_nb[1].notifier_call = vbus_cable1_evt;
>>>>>>     data->vbus_nb[2].notifier_call = vbus_cable2_evt;
>>>>>>     for (i = 0; i < ARRAY_SIZE(vbus_cable_ids); i++) {
>>>>>>         ret = devm_extcon_register_notifier(dev, data->vbus_extcon,
>>>>>>                     vbus_cable_ids[i], &data->vbus_nb[i]);
>>>>>>         if (ret)
>>>>>>             ...
>>>>>>     }
>>>>>> }
>>>>>
>>>>> You can get the notification for multiple external connector
>>>>> by using the only one notifier_block as following:
>>>>>
>>>>> static const unsigned int vbus_cable_ids[] = {
>>>>>     EXTCON_CHG_USB_SDP, EXTCON_CHG_USB_CDP, EXTCON_CHG_USB_DCP };
>>>>>
>>>>> struct driver_data {
>>>>>     struct notifier_block vbus_nb;
>>>>> }
>>>>>
>>>>> static int vbus_cable_evt(struct notifier_block *nb, unsigned long e, void *p)
>>>>> {
>>>>>     struct driver_data *data =
>>>>>         container_of(nb, struct driver_data, vbus_nb);
>>>>>     int sdp_state, cdp_state, dcp_state;
>>>>>
>>>>>     sdp_state = extcon_get_state(data->vbus_extcon, EXTCON_CHG_USB_SDP);
>>>>>     cdp_state = extcon_get_state(data->vbus_extcon, EXTCON_CHG_USB_CDP);
>>>>>     dcp_state = extcon_get_state(data->vbus_extcon, EXTCON_CHG_USB_DCP);
>>>>>
>>>>>     ...
>>>>> }
>>>>>
>>>>> int probe(...)
>>>>> {
>>>>>     /* Register for vbus notification */
>>>>>     data->vbus_nb.notifier_call = vbus_cable_evt;
>>>>>     for (i = 0; i < ARRAY_SIZE(vbus_cable_ids); i++) {
>>>>>         ret = devm_extcon_register_notifier(dev, data->vbus_extcon,
>>>>>                     vbus_cable_ids[i], &data->vbus_nb);
>>>>>         if (ret)
>>>>>             ...
>>>>>     }
>>>>> }
>>>>
>>>> No that will not work, you cannot add the same notifier_block to 3
>>>> different notifier_heads, the list_head can only be part of one list!
>>>>
>>>> Also see:
>>>>
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/power/supply?id=577b1f06e22057e9cdc14b1ee5bd25435c71ff0f
>>>>
>>>> Which actually fixes an issue I encountered exactly because of doing
>>>> the above.
>>>>
>>>> So we really need something like my patch to make this simpler
>>>> and to remove the ugliness we currently have in axp288_charger.c
>>>> because of this problem (and are about to have in more drivers
>>>> I'm upstreaming). Also note that my patch is quite simple, the
>>>> amount of lines it adds is way less then the amount of lines
>>>> it will allow to remove in a single driver!
>>>
>>> Ping ?
>>>
>>> As explained this is a real problem and we really need a proper solution
>>> for this. I'm about to upstream 2 more drivers which need to monitor
>>> an antire extcon rather then a single cable on it, and I do not want
>>> to have to add hacks like this:
>>>
>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/power/supply?id=577b1f06e22057e9cdc14b1ee5bd25435c71ff0f
>>>
>>> To both drivers. My patch is IMHO a nice and clean solution for this,
>>> can you please merge this or provide an alternative solution ?
>>
>>
>> As you said, when using one notifier_block for multiple external connector,
>> it has a problem. But, it is not only for extcon framework. It depends
>> on the notifier_block code. If each external connector uses the
>> each notifier_block (it is a not hack), there is no any problem.
>>
>> As I already said on my reply[1] as following,
>> ---------------------------------------------
>> The extcon_register_notifier() function must support the notification
>> for only one external connector.
>> [1] https://www.spinics.net/lists/kernel/msg2468906.html
>> ---------------------------------------------
>>
>> I agree that the EXTCON needs to support the notification
>> for all supported external connector of extcon device
>> by using only one notifier_chain.
>>
>> I don't prefer to use the '-1' as the unique id for getting the
>> notification for all external connectors. Each argument of function
>> must have the correct meaning.
>>
>> I think that thanks for your report and suggestion.
>>
>> I'm considering to add the new function as following:
>> Following function will support the all external connector for notification
>> and the function argument don't include the unique id for external connector.
>> - extcon_regiter_all_notifier(struct extcon_dev *edev, struct notifier_block *nb);
>> (The function name is not fixed)
> 
> Adding a new extcon_register_all_notifier function for this is fine with
> me, shall I send a new patch for this ?

I'll develop the new following functions with your reported-by.

int extcon_register_notifier_all(struct extcon_dev *edev,
                               struct notifier_block *nb);
int extcon_unregister_notifier_all(struct extcon_dev *edev,
                               struct notifier_block *nb);
int devm_extcon_register_notifier_all(struct device *dev,
                               struct extcon_dev *edev,
                               struct notifier_block *nb);
void devm_extcon_unregister_notifier_all(struct device *dev,
                               struct extcon_dev *edev,
                               struct notifier_block *nb);


> 
> Regards,
> 
> Hans
> 
> 
> 
> 
>>
>>
>>>
>>> Regards,
>>>
>>> Hans
>>>
>>>
>>>
>>>
>>>>
>>>> Regards,
>>>>
>>>> Hans
>>>>
>>>>
>>>>>>
>>>>>> And then in the event handling the driver often checks the state of
>>>>>> all cables explicitly using extcon_get_state, rather then using the
>>>>>> event argument to the notifier_call.
>>>>>>
>>>>>> This commit makes extcon_[un]register_notifier accept -1 as cable-id,
>>>>>> which will cause the notifier to get called for changes on any cable
>>>>>> on the extcon_dev. Compared to the above example code this allows much
>>>>>> simpler code in drivers which want to monitor multiple cable types.
>>>>>>
>>>>>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>>>>>> ---
>>>>>> Changes in v2:
>>>>>> -Fix false-positive "warning: 'idx' may be used uninitialized" warning
>>>>>>  seen with some compiler versions
>>>>>> ---
>>>>>>  drivers/extcon/extcon.c | 35 ++++++++++++++++++++++++++---------
>>>>>>  drivers/extcon/extcon.h |  1 +
>>>>>>  2 files changed, 27 insertions(+), 9 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/extcon/extcon.c b/drivers/extcon/extcon.c
>>>>>> index 09ac5e7..2a042ee 100644
>>>>>> --- a/drivers/extcon/extcon.c
>>>>>> +++ b/drivers/extcon/extcon.c
>>>>>> @@ -449,6 +449,7 @@ int extcon_sync(struct extcon_dev *edev, unsigned int id)
>>>>>>
>>>>>>      state = !!(edev->state & BIT(index));
>>>>>>      raw_notifier_call_chain(&edev->nh[index], state, edev);
>>>>>> +    raw_notifier_call_chain(&edev->nh_all, 0, edev);
>>>>>>
>>>>>>      /* This could be in interrupt handler */
>>>>>>      prop_buf = (char *)get_zeroed_page(GFP_ATOMIC);
>>>>>> @@ -900,6 +901,8 @@ EXPORT_SYMBOL_GPL(extcon_get_extcon_dev);
>>>>>>   *                any attach status changes from the extcon.
>>>>>>   * @edev:    the extcon device that has the external connecotr.
>>>>>>   * @id:        the unique id of each external connector in extcon enumeration.
>>>>>> + *        or -1 to get notififications for all cables on edev, in this
>>>>>> + *        case no state info will get passed to the notifier_call.
>>>>>>   * @nb:        a notifier block to be registered.
>>>>>>   *
>>>>>>   * Note that the second parameter given to the callback of nb (val) is
>>>>>> @@ -915,12 +918,18 @@ int extcon_register_notifier(struct extcon_dev *edev, unsigned int id,
>>>>>>      if (!edev || !nb)
>>>>>>          return -EINVAL;
>>>>>>
>>>>>> -    idx = find_cable_index_by_id(edev, id);
>>>>>> -    if (idx < 0)
>>>>>> -        return idx;
>>>>>> +    if ((int)id != -1) {
>>>>>> +        idx = find_cable_index_by_id(edev, id);
>>>>>> +        if (idx < 0)
>>>>>> +            return idx;
>>>>>> +    }
>>>>>>
>>>>>>      spin_lock_irqsave(&edev->lock, flags);
>>>>>> -    ret = raw_notifier_chain_register(&edev->nh[idx], nb);
>>>>>> +    if ((int)id != -1)
>>>>>> +        ret = raw_notifier_chain_register(&edev->nh[idx], nb);
>>>>>> +    else
>>>>>> +        ret = raw_notifier_chain_register(&edev->nh_all, nb);
>>>>>> +
>>>>>>      spin_unlock_irqrestore(&edev->lock, flags);
>>>>>>
>>>>>>      return ret;
>>>>>> @@ -937,17 +946,23 @@ int extcon_unregister_notifier(struct extcon_dev *edev, unsigned int id,
>>>>>>                  struct notifier_block *nb)
>>>>>>  {
>>>>>>      unsigned long flags;
>>>>>> -    int ret, idx;
>>>>>> +    int ret, idx = 0;
>>>>>>
>>>>>>      if (!edev || !nb)
>>>>>>          return -EINVAL;
>>>>>>
>>>>>> -    idx = find_cable_index_by_id(edev, id);
>>>>>> -    if (idx < 0)
>>>>>> -        return idx;
>>>>>> +    if ((int)id != -1) {
>>>>>> +        idx = find_cable_index_by_id(edev, id);
>>>>>> +        if (idx < 0)
>>>>>> +            return idx;
>>>>>> +    }
>>>>>>
>>>>>>      spin_lock_irqsave(&edev->lock, flags);
>>>>>> -    ret = raw_notifier_chain_unregister(&edev->nh[idx], nb);
>>>>>> +    if ((int)id != -1)
>>>>>> +        ret = raw_notifier_chain_unregister(&edev->nh[idx], nb);
>>>>>> +    else
>>>>>> +        ret = raw_notifier_chain_unregister(&edev->nh_all, nb);
>>>>>> +
>>>>>>      spin_unlock_irqrestore(&edev->lock, flags);
>>>>>>
>>>>>>      return ret;
>>>>>> @@ -1212,6 +1227,8 @@ int extcon_dev_register(struct extcon_dev *edev)
>>>>>>      for (index = 0; index < edev->max_supported; index++)
>>>>>>          RAW_INIT_NOTIFIER_HEAD(&edev->nh[index]);
>>>>>>
>>>>>> +    RAW_INIT_NOTIFIER_HEAD(&edev->nh_all);
>>>>>> +
>>>>>>      dev_set_drvdata(&edev->dev, edev);
>>>>>>      edev->state = 0;
>>>>>>
>>>>>> diff --git a/drivers/extcon/extcon.h b/drivers/extcon/extcon.h
>>>>>> index 993ddcc..2e6c09d 100644
>>>>>> --- a/drivers/extcon/extcon.h
>>>>>> +++ b/drivers/extcon/extcon.h
>>>>>> @@ -44,6 +44,7 @@ struct extcon_dev {
>>>>>>      /* Internal data. Please do not set. */
>>>>>>      struct device dev;
>>>>>>      struct raw_notifier_head *nh;
>>>>>> +    struct raw_notifier_head nh_all;
>>>>>>      struct list_head entry;
>>>>>>      int max_supported;
>>>>>>      spinlock_t lock;    /* could be called by irq handler */
>>>>>>
>>>>>
>>>>>
>>>
>>>
>>
>>
> 
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

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