Re: [RFC/PATCH 0/2] u_char.c and mtp.c patches

[Roger Quadros <roger.quadros@nokia.com>]

ext Linus Walleij wrote:
> 2010/4/19 Steve Calfee <stevecalfee@gmail.com>:
> 
>> For 6 months, a while ago, I was working on virtual USB stuff for a
>> company. I did analyser traces of many devices including many MS
>> devices (mice, webcam, keyboard, joystick), and never found any device
>> from MS or anyone that supported that command. All devices that I saw
>> just replied (properly) with a STALL - and Winxp would just continue
>> on and handle the device.
> 
> I don't think they add it to that kind of devices. Only MTP players
> for what I've seen. Maybe some weirdo RNDIS stuff use it too?
> 
> But as you see Windows issues this command to absolutely everything
> you plug in, I've been thinking about how we could emulate the same
> behaviour in Linux but actually I think it's a bit insane and only take
> extra time to send that command to whatever you plug in.
> 
> Still it would be nice to know directly from userspace if a device that
> was plugged in was MTP or not, especially we need this for udev
> rules (or HAL, DeviceKit etc, whatever) that want to make the device
> read/writable for the console user when it's plugged in.
> 
>> When you say "older windowses", which one; the only earlier ones with
>> USB was 98 and descendants and somewhat 95.
> 
> Especially the Win98 and Win2000 stuff that comes with the Windows
> Media Player has to respond to it.
> 
> Actually Windows probably has some internal list of devices and
> specific quirks it has to use for them to work properly, but I'm not
> sure. (I asked them about it I think, but didn't get any replies.)
> 
>> Also have you found a device that actually responds to the "get
>> osdescriptor" request?
> 
> Almost all MTP devices out there does, check the logs here:
> http://libmtp.cvs.sourceforge.net/viewvc/libmtp/libmtp/logs/
> 
> If the device responds with something sane for command 0xee
> the MTP stack will go on to issue special commands, you can find
> our code for this here:
> http://libmtp.cvs.sourceforge.net/viewvc/*checkout*/libmtp/libmtp/src/libusb-glue.c?revision=1.284
> 

Do you know if these older Windows OSes request the OS descriptor when the 
device uses a standard USB class code?

AFAIK the MTP device device should use PTP Class, Subclass and protocol codes 
(i.e. 6:1:1). In this case Windows XP treats it as a PTP device (even if the 
device implements OS descriptors).
I'm sure all MTP devices in the market that implement OS descriptors use Vendor 
Specific class (i.e. 0xff:0:0) which is not the right thing to do after MTP has 
been standardized by usb.if.

cheers,
-roger