RE: [RFCv1 1/1] USB: EHCI: Do not return -EPIPE when hub is disconnected

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, 5 Dec 2019, Erkka Talvitie wrote:

> I tested this change and the issue did not reproduce.
> 
> However when I was writing the comments for the patch I started to think
> what happens in this following scenario:
> 
> The PID Code is IN.
> 
> 1. First there will be XACT, the CERR is decremented, let's say from 3 to 2
> and the host controller executes a retry.
> 2. On this next try there will happen the condition mentioned in the Table
> 4-13 of the EHCI specification so that the MMF is set and the queue is
> halted (because it is IN).
> 3. To my understanding now the execution enters to this first stall check
> if, as CERR is > 0 and CERR < EHCI_TUNE_CERR.
> 4. The -EPIPE (stall) is returned when actually the queue was halted due to
> MMF - not stall - and the -EPROTO should be returned.
> 
> Is my logic correct or am I missing something?

The same thought had occurred to me.

> If you agree with me then I would like to present you a bit more bold (in a
> sense of amount of refactoring) RFC. In high level this another RFC
> separates 1. error check and 2. stall check. For me this approach is a bit
> easier to understand from the code. Or then please  propose another
> solution.

I was going to suggest: Just check for MMF and PID == IN before
checking for STALL.  Everything else can remain the way it is.

Alan Stern