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Date:      Tue, 28 Jul 2009 19:40:27 +0400
From:      Eygene Ryabinkin <>
Subject:   Re: usb/137189: [usb][patch] create and use sysctl nodes for HID report descriptors
Message-ID:  <zwXGioeg7oGpbCtzpfQAMfews68@CWODRlDR5RMqbkBfR0/UzHcfNhE>
In-Reply-To: </kNvT4PUQiAaILwpSOAKI37SlXY@CWODRlDR5RMqbkBfR0/UzHcfNhE>
References:  <> <> <8RwwU1KLz1ezvFiU9HsY6uoNfkU@nflB3XSqYRRHWdyVHMOFGnCK5Pk> </kNvT4PUQiAaILwpSOAKI37SlXY@CWODRlDR5RMqbkBfR0/UzHcfNhE>

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HPS wrote:
> > I can, but how to relate the device name under devfs to the descriptor
> > to be retrieved?
> By unit number and device address, like usbconfig.

Yes, but these numbers are the ugen ones; on my system, for example,
ums0 maps to ugen5.3.0.

>>  I can enumerate all HID descriptors via libusb, but I
> > can't currently say which device uses them.
> Try:
> usbconfig show_ifdrv

Yes, that's better.  But can I rely that the first item in the output of
the libusb20_dev_get_iface_desc() will be the device name?  And still,
to get the report descriptor from one device, I should walk the entire
USB tree until I'll find the device I am interested in.  May be there
are some other ways?  I understand that enumeration is the principle of
the USB bus, but may be there are another ways to directly grab 'struct
libusb20_device *' or alike for the devfs node I am interested in?

> > Why do you dislike the sysctl approach? It is simple and reliable.
> It's duplicating access to data. There is not that much wrong about
> it, except it will not work if the device is of another kind. I.E. you
> would have to patch the HID sysctl node into every driver accessing
> HID descriptors?

Just now -- yes, I'll need it.  But probably I can move this
functionality into the USB bus level -- it will automatically create
this sysctl node for all HID children and will dispose it on the detach.
usb_probe_and_attach() is a candidate for such functionality.  Will it
be bad?
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