Re: [PATCH v2 0/2] extcon: Inform the state of both ID and VBUS pin for USB
From: Roger Quadros
Date: Tue Jun 02 2015 - 02:52:12 EST
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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