Re: some question about period scheduleing

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On Fri, 13 Dec 2013, vichy wrote:

> hi
> 
> 2013/12/2 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>:
> > On Sun, 1 Dec 2013, vichy wrote:
> >
> >> hi Alan:
> >>
> >> 2013/12/1 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>:
> >> > On Fri, 29 Nov 2013, vichy wrote:
> >> >
> >> >> hi all:
> >> >> My connection like below
> >> >> ehci --> high speed hub -> full speed device
> >> >>
> >> >> I have some questions about period scheduling.
> >> >> 1. when creating  qh for full speed device,  why we set EHCI_TUNE_RL_TT.
> >> >
> >> > Are you asking why EHCI_TUNE_RL_TT is equal to 0?  I don't know -- it
> >> > looks like a mistake.  Do you find that changing it to 3 makes any
> >> > difference?
> >> Yes, when I change EHCI_TUNE_RL_TT as not 0.
> >> The transaction can keep going.
> >
> > But if EHCI_TUNE_RL_TT is 0, the transfer doesn't work?
> No. the transaction will stop since device return Nak.
> I copy the usb traffic log for your reference.

The device did not return NAK.  The NAK was sent by the high-speed hub
the device was attached to.

> usually device will not return NAK in setup token. but in my case, it did.

When EHCI_TUNE_RL_TT is set to 0, the controller should never stop
retrying the transfer.  That's what 0 means here -- 3 means stop
(temporarily) after 3 attempts, but 0 means never stop.

This sounds like a bug in your EHCI hardware.  What type of controller 
are you using?

Anyway, I don't mind changing EHCI_TUNE_RL_TT to 3.  Would you like to 
submit a patch?

Alan Stern

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