Dear all, On 05/29/2015 07:53 PM, Chanwoo Choi wrote: > 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 >
On last month, Robert Baldyga sent the patch[1] for extcon-usb-gpio driver. [1] https://lkml.org/lkml/2015/4/2/311 - [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection This patch[1] included a following table which show the type of external connectors according to both ID and VBUS pin state. State | ID | VBUS ---------------------------------------- [1] USB | H | H [2] none | H | L [3] USB & USB-HOST | L | H [4] USB-HOST | L | L So, I think that extcon-usb-gpio.c could set below two status with set: - the state of whether USB/USB-HOST are attached or detached -> send the state to both kernel-space and user-space. : extcon_set_cable_state_() - the h/w line state of both ID and VBUS pin state -> send the state to only kernel space. : extcon_set_cable_line_state() [1] State | ID | VBUS ---------------------------------------- [1] USB | H | H extcon_set_cable_state_(edev, EXTCON_USB, true); extcon_set_cable_state_(edev, EXTCON_USB_HOST, false); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_ID_HIGH); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_VBUS_HIGH); [2] State | ID | VBUS ---------------------------------------- [2] none | H | L extcon_set_cable_state_(edev, EXTCON_USB, false); extcon_set_cable_state_(edev, EXTCON_USB_HOST, false); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_ID_HIGH); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_VBUS_LOW); [3] State | ID | VBUS ---------------------------------------- [3] USB & USB-HOST | L | H extcon_set_cable_state_(edev, EXTCON_USB, false); extcon_set_cable_state_(edev, EXTCON_USB_HOST, true); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_ID_LOW); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_VBUS_HIGH); [4] State | ID | VBUS ---------------------------------------- [4] USB-HOST | L | L extcon_set_cable_state_(edev, EXTCON_USB, false); extcon_set_cable_state_(edev, EXTCON_USB_HOST, true); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_ID_LOW); extcon_set_cable_line_state(edev, EXTCON_USB, EXTCON_USB_VBUS_LOW); If I know the wrong knowledge, please let me know your comment and advice. 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/
