Messages in this thread | | | Date | Fri, 29 May 2015 09:22:27 +0800 | From | Peter Chen <> | Subject | Re: [PATCH v2 0/2] extcon: Inform the state of both ID and VBUS pin for USB |
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On Thu, May 28, 2015 at 05:23:57PM +0300, Roger Quadros wrote: > +Peter & Li, > > Ivan, > > On 28/05/15 11:45, Ivan T. Ivanov wrote: > > > >Hi Chanwoo, > > > >On Wed, 2015-05-27 at 21:15 +0900, Chanwoo Choi wrote: > >>Previously, I discussed how to inform the changed state of both ID > >>and VBUS pin for USB connector on patch-set[1]. > >>[1] https://lkml.org/lkml/2015/4/2/310 > >> > >>So, this patch adds the extcon_set_cable_line_state() function to inform > >>the additional state of external connectors without additional register/ > >>unregister functions. This function uses the existing notifier chain > >>which is registered by extcon_register_notifier() / extcon_register_interest(). > >> > >>The extcon_set_cable_line_state() can inform the new state of both > >>ID and VBUS pin state through extcon_set_cable_line_state(). > >> > >>For exmaple: > >>- On extcon-usb-gpio.c as extcon provider driver as following: > >> static void usb_extcon_detect_cable(struct work_struct *work) > >> { > >> ... > >> /* check ID and update cable state */ > >> id = gpiod_get_value_cansleep(info->id_gpiod); > >> if (id) { > >> extcon_set_cable_state_(info->edev, EXTCON_USB_HOST, false); > >> extcon_set_cable_state_(info->edev, EXTCON_USB, true); > >> > >> extcon_set_cable_line_state(info->edev, EXTCON_USB, > >> EXTCON_USB_ID_HIGH); > > > >I am getting more and more confused :-). Why EXTCON_USB is now used for ID notifications? > >It should be EXTCON_USB_HOST, no? Why we need another function, framework already have > >required information from the function one line above, do I miss something? > > This is because the existing EXTCON_USB_HOST and EXTCON_USB do not capture all > the 4 states of ID and VBUS pins that we need for a real USB driver to work. > > It looks like it was designed from user space users perspective where they are > only interested in USB role. i.e. host or peripheral. > > Right now we are mixing both ID/VBUS and HOST/Peripheral states. > This will break when we consider OTG role switching. > With role switching, the USB device might start as a peripheral but switch role to host > on the fly and the existing setup (including these patches) can't cater to that > if user space is relying on EXTCON_USB_HOST/EXTCON_USB events. > Because they are hard-wired to the ID pin state which doesn't change during > role switch without cable switch. > > The USB driver doesn't care about EXTCON_USB_HOST/peripheral states. > It just needs ID/VBUS states and should decide the Host/Peripheral state from > that and other inputs (like HNP/user request/etc). > > The flow could be like this > > (extcon-usb-driver) -> [ID/VBUS states] -> (USB driver) -> [HOST/Peripheral states]
Agree. Chanwoo, USB driver knows better than extcon driver about USB role (host/peripheral), so the app should use USB interface to know it, in fact, I don't be aware any use case needs to know USB role? Are there any users for EXTCON_USB and EXTCON_USB_HOST currently?
> > If that is not going to happen then we will have to switch to this > > (usb phy driver) -> [ID/VBUS states] -> (USB driver) -> (extcon f/w) -> [Host/Peripheral states] > > > Felipe, Peter, Li, > > what do you guys suggest? > > cheers, > -roger > > > > >> } else { > >> extcon_set_cable_state_(info->edev, EXTCON_USB, false); > >> extcon_set_cable_state_(info->edev, EXTCON_USB_HOST, true); > >> > >> extcon_set_cable_line_state(info->edev, EXTCON_USB, > >> EXTCON_USB_ID_LOW); > >> } > >> } > >> > >>- On specific extcon consumder driver as following: > >> static int xxx_probe(struct platform_device *pdev) > >> { > >> struct notifier_chain nh; > >> > >> nb.notifier_call = extcon_usb_notifier; > >> ret = extcon_register_notifier(edev, EXTCON_USB, &nb); > > > >This is bit misleading. 'nb' could not be in stack. > > > >Regards, > >Ivan > >
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Best Regards, Peter Chen
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