On Wed, 1 Mar 2006, Marc Singer wrote:

> I'm going through the code paths and finding that the reason it stalls
> on DESCRIPTOR requests is that that is all it can do.  It only
> processes a couple of different types of setup messages, DESCRIPTORS
> are not among them.

Be careful when you say things like that.  What does the word "it" refer 
to -- the UDC driver or the gadget driver?  In general, UDC drivers don't 
respond to many requests at all; they forward everything to the gadget 
driver.

> What's perplexing me is responses like this:
> 
>    0:33.300555 # 16  s> Ci 009:00 s 80 06 0200 0000 0400 ( DtH st dv 
> GET_DESCRIPTOR [CONFIGURATION 0] ) --- 1024 <
> ...
>    0:33.322552 # 16 <c  Ci 009:00 --- -121 32 = 09022000 0103fac0 01090400 
> 0002ff00 00fa0705 02024000 00070581 02400000
> 
> What is the -121?  For that matter, what are the -32's?  There is a
> lot of time between these messages.  Is the data stream being
> corrupted and, therefore, I just need to check on the memory
> allocation and queuing?

Look up in the numerical values in include/asm-generic/errno*.h.  You'll
find that -121 is EREMOTEIO and -32 is -EPIPE.  Then look up the error
codes in Documentation/usb/error-codes.txt.  You'll find that -EREMOTEIO 
means the data transfer was shorter than expected and -EPIPE means the 
endpoint was stalled.

Alan Stern



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