netdev - Re: [PATCH 0/2] Fix couple of issues with 'ethtool' get/set API's

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Date:	Mon, 01 Jun 2015 19:07:13 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Arun Parameswaran <aparames@...adcom.com>
Cc:	Ben Hutchings <bwh@...nel.org>, netdev@...r.kernel.org,
	jdzheng@...adcom.com
Subject: Re: [PATCH 0/2] Fix couple of issues with 'ethtool' get/set API's

On Mon, 2015-06-01 at 10:14 -0700, Arun Parameswaran wrote:
> On 15-05-31 12:59 PM, Ben Hutchings wrote:
> > On Fri, 2015-05-22 at 15:43 -0700, Arun Parameswaran wrote:
> >> Hi,
> >> The patch fixes 2 issues with 'ethtool' getting/setting parametres in
> >> the do_gset() do_sset() API's.
> >>
> >> I have pushed a patch to the Kernel to fix an issue in the handling of
> >> the 'ethtool' commands which got accepted.
> >> This Kernel patch was based on Linux v4.1-rc4 and is available in:
> >> https://github.com/Broadcom/cygnus-linux/tree/net-core-ethtool-fix-v1
> >>
> >> The Kernel was always clearing the command from the 'ethtool' resulting
> >> in all operations to deal with PHY0. This prevents querying/setting
> >> PHY 1's settings.
> > [...]
> > 
> > Each net device can be associated with a single PHY at a time, and the
> > ETHTOOL_GSET implementation should fill in the PHY address in the
> > ethtool_cmd::phy_address field.  Where there are multiple PHYs that can
> > be connected to the net device's MAC, an ETHTOOL_SSET operation can be
> > used to change that PHY address.
> > 
> The above can be done by the driver when there is one PHY per MAC. In our
> case we have multiple PHYs controlled by the same MAC. I should have
> clarified this earlier, I apologize.

I understand that you can have multiple PHYs on the same MDIO bus, but
not how the MAC can use them at the same time.  Is this hardware level
bonding?  Or are multiple PHYs needed for a single link?

> When we specify the 'phyad', in the command line, we were expecting the
> 'ethtool' to fetch/set data for that 'phyad'. This is the intend of the
> patch.
> 
> With the patch (in 'ethtool' and Kernel), if 'phyad' is not specified, it
> will still function as you described above, it will be up to the driver to
> return the proper 'phyad' and related settings.
[...]

But without the patch in ethtool and other programs calling this API
(it's not just the ethtool command!), you get random junk as the
phy_address.  How will you tell whether it's valid or not?

Ben.

-- 
Ben Hutchings
Power corrupts.  Absolute power is kind of neat.
                           - John Lehman, Secretary of the US Navy 1981-1987

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