Messages in this thread | | | Date | Tue, 2 Jun 2015 09:51:41 +0300 | From | Roger Quadros <> | Subject | Re: [PATCH v2 0/2] extcon: Inform the state of both ID and VBUS pin for USB |
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Chanwoo,
On 29/05/15 15:15, Chanwoo Choi wrote: > 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.
I don't see any issues with extcon_get_cable_line_state(). I would prefer that than changing existing APIS.
User space users will still fail in the dynamic role swap case [3]. But probably nobody cares about it as nobody seems to be complaining or using role-swap :) So we can choose to ignore that and solve it when someone complains.
cheers, -roger
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