Re: [PATCH] usb: udc: add gadget state kobject uevent

[Rong Wang]

Hi Peter,


On Wed, Jul 17, 2013 at 10:36 AM, Peter Chen <peter.chen@xxxxxxxxxxxxx> wrote:
> On Mon, Jul 15, 2013 at 11:31:17PM -0700, Greg KH wrote:
>> On Tue, Jul 16, 2013 at 11:49:07AM +0800, Rong Wang wrote:
>> > Hi Greg,
>> >
>> > The USB on our platform can change roles between HOST and GADGET, but
>> > it is not capable of OTG.
>>
>> That kind of sounds like the definition of OTG :)
>>
>> > When the USB changes between roles the udev will run some scripts
>> > automatically according to the udev rules.
>>
>> What exactly does udev/userspace see when the roles change?
>>
>> And what can trigger the change in roles?
>>
>> > The default role is GADGET, and we bind the g_mass_storage to the USB
>> > GADGET role.
>> >
>> > We should secure the back end file storage between the device and the
>> > host PC connecting to our device.
>> > We need to know when the GADGET is really connect to a host PC, then
>> > we can umount the file on the device
>> > and export it to the g_mass_storage.
>>
>> I thought you already get an event for this, otherwise no one would be
>> able to properly deal with this.
>>
>> > The question is since we default GADGET, so the g_mass_storage.ko is
>> > installed early but connecting to a host PC
>> > is randomly, But the udev has no idea when a host PC connects our device.
>> >
>> > So we consider it's reasonable to let the udev know the GADGET device state.
>> > Is there any alternative to our question?
>>
>> I thought we already export events for gadget device states, have you
>> looked for them?  I can't dig through the code at the moment, but this
>> seems like a pretty common issue...
>>
>
> If I understand correctly,  what Rong wants is udev can be notified the
> udc state changes, like connect/disconnect event. Currently, we only
> export it to /sys.

OK. Thanks for your share.

And you develop a new utility rather than udev to monitor that file?
And you probably create a work queue in your udc driver to do this work?

>
> --
>
> Best Regards,
> Peter Chen
>
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