Re: nfe(4) for nVidia GigE

["Sepherosa Ziehau" <sepherosa@xxxxxxxxx>]

On 8/27/06, Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx> wrote:
> :Yeah, that's it!!  Thank you very much!!  I didn't figure out the real
> :cause in the old version, but instead went to the sidetrack: adding a
> :delay in nfe_encap() :-P
> :
> :Best Regards,
> :sephe
>
>     It would be nice if we could determine which fix was the one that
>     fixed your MB.  Insofar as I can tell there are three possible
>     causes for the watchdog timeouts.
>
>     (1) The hardware races the setting of NFE_TX_VALID in the second ring
>         buffer of a multi-buffer TX DMA.  That is, the hardware is actively
>         transmitting a prior packet and the driver starts laying down the
>         new packet, and the hardware starts trying to transmit the new
>         packet before the driver can finish laying it down.  This is due
>         to the driver improperly setting NFE_TX_VALID on the first ring
>         buffer in the new packet before finishing setting up all the ring
>         buffers.
>
>         Your delay had the effect of allowing the hardware to finish up
>         all the TX ring buffers and thus be quiescent when new packets
>         get queued, avoiding the race.  Insofar as I can tell when you
>         KICK the hardware it runs TX ring buffers until it sees one
>         without NFE_TX_VALID set, then it goes quiescent until the next
>         KICK.
>
>         This is solved by the encap code fixes.

This one fixes my MB's watchdog timeout problem :-)

>     (2) The hardware fails to generate a TX completion interrupt.  The
>         watchdog comes along and decides to reset the interface.
>
>         This is solved by the fixes in the watchdog code which first attempt
>         to drain the TX ring and then KICK it again before giving up and
>         resetting the interface (which doesn't solve the problem anyhow, it
>         appears).  The KICK seemed to get TX completion interrupts working
>         again.

Do you mean after the KICK in watchdog handler, normal TX intr
behaviour restores?  mmm, IMHO, that means our TX descs are setup
properly, but some unknown registers are not setup properly, or it may
be a hardware bug :P

Best Regards,
sephe

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