Re: [PATCH v2 2/4] e1000e: Do not read icr in Other interrupt

[Alexander Duyck]

On 11/04/2015 03:19 PM, Benjamin Poirier wrote:
> On 2015/10/30 12:19, Alexander Duyck wrote:
> > On 10/30/2015 10:31 AM, Benjamin Poirier wrote:
> > > Using eiac instead of reading icr allows us to avoid interference with
> > > rx and tx interrupts in the Other interrupt handler.
> > >
> > > According to the 82574 datasheet section 10.2.4.1, interrupt causes that
> > > trigger the Other interrupt are
> > > 1) Link Status Change.
> > > 2) Receiver Overrun.
> > > 3) MDIO Access Complete.
> > > 4) Small Receive Packet Detected.
> > > 5) Receive ACK Frame Detected.
> > > 6) Manageability Event Detected.
> > >
> > > Causes 3, 4, 5 are related to features which are not enabled by the
> > > driver. Always assume that cause 1 is what triggered the Other interrupt
> > > and set get_link_status. Cause 2 and 6 should be rare enough that the
> > > extra cost of needlessly re-reading the link status is negligible.
> > >
> > > Signed-off-by: Benjamin Poirier <bpoirier@xxxxxxxx>
> > You might want to instead use a write of LSC to the ICR instead of just
> > using auto-clear and not enabling LSC.  My concern is that you might no
> > longer be getting link status change events at all.  An easy test is to just
> > unplug/plug the cable a few times, or run "ethtool -r" on the link partner
> > if connected back to back.  You should see messages appear in the dmesg log
> > indicating that the link state changed.
> >
> > In addition you should probably clear the IAME bit in the CTRL_EXT register
> > so that you don't risk masking the interrupts on the ICR read or write.
> Thanks, your concern about not getting LSC events was right. After more
> experimentation I noticed that in order for the Other interrupt to be
> raised for each of these six conditions, the IMS bit for that condition
> must also be set. I've restored setting LSC in IMS. OTOH, I don't see a
> need to clear LSC from ICR. Even without an ICR read or write-to-clear
> to clear the LSC bit, Other interrupts are raised to signal LSC events.
>
> I'll wait for net-next to reopen and send v3.

You probably don't need to wait.  The Intel-wired tree operates outside 
of Dave's merge window, and it will take some time for the patches to be 
validated before the Jeff can submit them to Dave.

- Alex
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