> On Nov 6, 2019, at 02:07, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, 6 Nov 2019, Kai-Heng Feng wrote:
>
>> On Dell WD15 dock, sometimes USB ethernet cannot be detected after plugging
>> cable to the ethernet port, the hub and roothub get runtime resumed and
>> runtime suspended immediately:
>> ...
>
>> ...
>>
>> As Mathias pointed out, the hub enters Cold Attach Status state and
>> requires a warm reset. However usb_reset_device() bails out early when
>> the device is in suspended state, as its callers port_event() and
>> hub_event() don't always resume the device.
>>
>> Since there's nothing wrong to reset a suspended device, allow
>> usb_reset_device() to do so to solve the issue.
>
> I was sure I remembered reading somewhere that suspended devices were
> not allowed to be reset, but now I can't find that requirement anywhere
> in the USB spec.
I don't find it in the USB spec either.
That said, the following usb_autoresume_device() before reset may resume the device.
I've also tried using pm_runtime_get_noresume() and it works equally well for my case but I am not sure if we want to change the behavior here.
>
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
>> ---
>> drivers/usb/core/hub.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index 05a2d51bdbe0..f0194fdbc9b8 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -5877,8 +5877,7 @@ int usb_reset_device(struct usb_device *udev)
>> struct usb_host_config *config = udev->actconfig;
>> struct usb_hub *hub = usb_hub_to_struct_hub(udev->parent);
>>
>> - if (udev->state == USB_STATE_NOTATTACHED ||
>> - udev->state == USB_STATE_SUSPENDED) {
>> + if (udev->state == USB_STATE_NOTATTACHED) {
>> dev_dbg(&udev->dev, "device reset not allowed in state %d\n",
>> udev->state);
>> return -EINVAL;
>
> You forgot to update the kerneldoc for this function.
Ok, will do that in v2.
Kai-Heng
>
> Alan Stern
>
