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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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