Re: [net-next 1/4 (V3)] net: ethtool: add the EEE support

[Ben Hutchings <bhutchings@solarflare.com>]

On Sun, 2012-04-29 at 12:20 +0300, Yuval Mintz wrote:
> On 04/27/2012 05:11 PM, Giuseppe CAVALLARO wrote:
> 
> > On 4/26/2012 7:17 PM, Ben Hutchings wrote:
> >> On Thu, 2012-04-26 at 09:48 +0200, Giuseppe CAVALLARO wrote:
> >>> Hello Ben
> >>>
> >>> On 4/19/2012 5:30 PM, Ben Hutchings wrote:
> >>> [snip]
> >>>>> I'm changing the code for getting/setting the EEE capability and trying
> >>>>> to follow your suggestions.
> >>>>>
> >>>>> The "get" will show the following things; this is a bit different of the
> >>>>> points "a" "b" and "c" we had discussed. Maybe, this could also be a
> >>>>> more complete (*) .
> >>>>> The ethtool (see output below as example) could report the phy
> >>>>> (supported/advertised/lp_advertised) and mac eee capabilities separately.
> >>>> Sounds reasonable.
> >>>>
> >>>>> The "set" will be useful for some eth devices (like the stmmac) that can
> >>>>> stop/enable internally the eee capability (at mac level).
> >>>> I don't know much about EEE, but shouldn't the driver take care of
> >>>> configuring the MAC for this whenever the PHY is set to advertise EEE
> >>>> capability?
> >>> Yes indeed this can be done at driver level. So could I definitely
> >>> remove it from ethtool? What do you suggest?
> >>>
> >>> In case of the stmmac I could add a specific driver option via sys to
> >>> enable/disable the eee and set timer.
> >> Generally, ethtool doesn't distinguish MAC and PHY settings because they
> >> have to be configured consistently for the device to do anything useful.
> >> If there is some good use for enabling EEE in the MAC and not the PHY,
> >> or vice versa, then this should be exposed in the ethtool interface.
> >> But if not then I don't believe it needs to be in either an ethtool or a
> >> driver-specific interface.
> > Thanks Ben for this clarification: in case of the stmmac the option is
> > useful to stop a timer to enter in lpi state for the tx.
> > So it's worth having that and from ethtool.

I think I finally get it.  If we negotiate a 100BASE-TX link (or one of
the various backplane modes) with EEE enabled, we allow the link partner
to assert LPI but we might still not want to assert it in the transmit
direction.  Right?  (Whereas for 1000BASE-T and 10GBASE-T this would be
useless, since both sides must assert LPI before any transition can
happen.)

> How will a user turn off EEE support using this implementation?

At the ethtool API level this would be done by clearing the EEE
advertising mask.  At the command-line level there could be a shortcut
for this, just as you can use 'autoneg on' and 'autoneg off' rather than
specifying a mask of link modes.

> Are you suggesting a "set" that works similarly to the control of the pause
> parameters - that is, a user could either shutdown EEE or only Tx, which
> will mean to the driver "don't enter Tx LPI mode"?
>
> Keep in mind that if later an interface controlling the LPI timers would be
> added (as a measure of user control to the power saving vs. latency issue),
> it could make this 'partial' closure interface redundant.
>
> Perhaps "set" should only turn the EEE feature on/off entirely (adv. them or
> not, since clearly the link will have to be re-established afterwards), and
> we should have a different function that prevents entry into LPI mode in Tx
> - one whose functionality could later on be extended.

It sounds like this might as well be included, even if not all
drivers/hardware would allow the values to be changed.  So the command
structure would have at least:

1. EEE link mode supported flags (get-only)
2. EEE link mode advertising flags (get/set)
3. Ditto for link partner (get-only)
4. TX LPI enable flag (get/set)
5. TX LPI timer values (get/set but driver may reject changes)

But if it's not yet clear exactly what timer parameters will be useful,
we could leave some reserved space and then later define them along with
flags to indicate whether the driver understands them.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.