On Wed, 12 Dec 2007, Phil Endecott wrote:

> I presume that reading /sys/bConfigurationValue just returns the 
> kernel's record of which configuration was most recently set, rather 
> than actually doing a get_configuration on the bus - doesn't it?

That's right.

> > Writing to the sysfs 
> > bConfigurationValue file doesn't have this requirement.
> 
> Ah, I didn't know that that was writeable.  Interesting.  Maybe there 
> is more that I can achieve by writing to sysfs.

None of the other files are writable except the ones in the .../power/ 
subdirectory and the "uevent" file.  You might want to look through the 
persist.txt and power-management.txt files under Documentation/usb/.

>  I'll have to think 
> about that.  Oh and BTW, there is also a sysfs file just called 
> 'configuration'; what does that do?

It contains the contents of the configuration's string descriptor.  If 
there isn't a config string descriptor then the file is empty.

Alan Stern

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