On Tue, Sep 21, 2010 at 12:12:57PM +0100, Toby Gray wrote:
> However there's clearly a reason for the call to usb_set_altinterface,
> so can anyone remember what devices it was necessary for?
It wasn't a specific device, it was all devices, I believe. It was to work
around a change in the kernel, which caused odd timeout issues. Also,
this fix made things work on Mac OSX and FreeBSD.
The usb_set_altinterface() call is the only one in libusb that
works directly with the interface, as far as I can tell.
You can read the long, painstaking thread here. I ended up doing
a git-bisect on the kernel to find the spot where it was having trouble.
http://marc.info/?t=123554440300001&r=1&w=2
Especially here, where Alan Stern says that calling set_altinterface()
should always be safe.
http://marc.info/?l=linux-usb&m=123627088604495&w=2
> Depending on the history of that call and what devices it was needed
> for, I'd suggest doing one of the following:
> 1) Removing the call to it entirely
> 2) Only call it if there are multiple alternate settings
> 3) Add it as an option for the various tools and API users
> 4) Carry on calling it but using a bAlternateSettings value retrieved
> from the device; this won't fix the mass storage issue but will fix the
> Barry code.
>
> What do people think?
I think someone needs to reproduce the original problem from 2009, and
see if option 2 would be a suitable fix, for Linux, Mac OSX, and FreeBSD. :-)
- Chris
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