On Wednesday 22 August 2012 10:00:12 Simon Farnsworth wrote:
> On Tuesday 21 August 2012 21:06:26 Henrik Rydberg wrote:
> > Hi Simon,
> >
> > > We're going through our collection of touch screens, making sure that they all
> > > work with current kernels, and we've found one that doesn't work with today's
> > > Linus master.
> > >
> > > lsusb describes the screen as:
> > > Bus 006 Device 002: ID 0408:3001 Quanta Computer, Inc. Optical Touch Screen
> >
> > What about 0408:3008, does that one work?
> >
> I don't have a sample of 0408:3008 to try.
>
> > > Any ideas on the best way to resolve this regression?
> >
> > What does 'cat /sys/bus/hid/devices/0003:0408:3001.0001/modalias' say?
>
> It's the same whether or not I revert the patch:
>
> # cat /sys/bus/hid/devices/0003:0408:3001.0001/modalias
> hid:b0003g0000v00000408p00003001
>
A look at the code said that the only way this could happen is if
hid_have_special_driver is set for this device, and no special driver claimed
it.
I've confirmed this by setting hid.ignore_special_devices to 1; it then works
unpatched.
The entry in the table is:
{ HID_USB_DEVICE(USB_VENDOR_ID_QUANTA, USB_DEVICE_ID_PIXART_IMAGING_INC_OPTICAL_TOUCH_SCREEN) },
This matches the device I have, and causes the problem behaviour.
It looks like the right thing to do is to audit the hid_have_special_driver
table, and confirm that there is an in-kernel special driver for every device
that has an entry.
--
Simon Farnsworth
Software Engineer
ONELAN Ltd
http://www.onelan.com
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