On Fri, Dec 12, 2014 at 9:21 AM, David Herrmann [off-list ref] wrote:

Hi

On Fri, Dec 12, 2014 at 6:18 PM, Andy Lutomirski [off-list ref] wrote:

quoted

On Dec 12, 2014 3:05 AM, "David Herrmann" [off-list ref] wrote:

quoted

So far, the solution is to use hid_device_io_start() and
hid_device_io_stop() in ->probe(). It's a hack to allow I/O during
->probe(). Maybe your idea is the way to go, but unless someone
implements it, we're stuck with the current code.

That should work.

For normal HID drivers (those that don't start IO from probe), what
happens if userspace starts IO before probe returns?  Does the driver
code prevent that somehow?

It's only the async hid intr channel that is affected by this.
User-space cannot trigger any outgoing I/O on the intr channel. Only
the synchronous ctrl channel via SET_REPORT can be triggered, but due
to the synchronous nature we always allow I/O on it.

I understand exactly one HID device, and that's U2F.  In U2F,
userspace will (directly or indirectly) use SET_REPORT, and the device
responds immediately (ish) using the async intr channel.

--Andy

Thanks
David

-- 
Andy Lutomirski
AMA Capital Management, LLC