Hi Peter, On 05/29/2015 10:22 AM, Peter Chen wrote: > 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?
You're right. But, extcon can just distinguish the type of external connectors and inform the type to the user-space and extcon consumer driver in kernel-space. When USB mouse or keyboard is attached, user-space can check the state of externel connector which is attaced to the H/W target as following: - /sys/class/extcon/extconX/cable.0/name -> USB - /sys/class/extcon/extconX/cable.0/state -> 0 - /sys/class/extcon/extconX/cable.1/name -> USB-HOST - /sys/class/extcon/extconX/cable.1/state -> 1 Thanks, Chanwoo Choi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/