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Hi Alan,
thanks a lot for your reply.
Alan Stern wrote:
> Your log annotations illustrate this misunderstanding. The "going down"
> and "coming back" parts have nothing to do with Setup vs. Data stages.
> Rather "going down" (or just S) means the message was Submitted to
> usbcore, and "coming back" (or just C) means that usbcore has Completed
> the message. And you got several lines labelled wrong; S always means
> Submit (or going down) and C always means Complete (or coming back).
>
You are so right, I was totally misreading the log. Now it makes more sense.
> Nothing special should be needed. Endpoint 0 should always be shared
> without difficulty.
>
> If necessary perhaps the ALSA driver could be patched to handle bogus
> 0-length responses, say by retrying the query?
>
> Alan Stern
>
Following your hint, I realized that ALSA's USB mixer interprets short
responses as valid ones and thus uses undefined values for further
calculations. I proposed a patch to the ALSA mailing list about that.
The Yealink P1K device now behaves mostly fine, but you are probably
right by suspecting the device getting confused somehow. Hammering EP0
with volume requests and key scan commands can suddenly turn the handset
into an unresponsive piece of plastic.
Thanks a lot for your advice.
-Thomas
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