Date:   Wed, 29 Mar 2017 09:38:35 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Chanwoo Choi <cw00.choi@...sung.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 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 ?

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 */
>>>>>
>>>>
>>>>
>>
>>
>
>

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