From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Doug Berger <opendmb@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
Florian Fainelli <f.fainelli@gmail.com>,
Heiner Kallweit <hkallweit1@gmail.com>,
bcm-kernel-feedback-list@broadcom.com, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 1/4] net: ethernet: validate pause autoneg setting
Date: Tue, 12 May 2020 19:55:03 +0100 [thread overview]
Message-ID: <20200512185503.GD1551@shell.armlinux.org.uk> (raw)
In-Reply-To: <ae63b295-b6e3-6c34-c69d-9e3e33bf7119@gmail.com>
On Tue, May 12, 2020 at 11:31:39AM -0700, Doug Berger wrote:
> This was intended as a fix, but I thought it would be better to keep it
> as part of this set for context and since net-next is currently open.
>
> The context is trying to improve the phylib support for offloading
> ethtool pause configuration and this is something that could be checked
> in a single location rather than by individual drivers.
>
> I included it here to get feedback about its appropriateness as a common
> behavior. I should have been more explicit about that.
>
> Personally, I'm actually not that fond of this change since it can
> easily be a source of confusion with the ethtool interface because the
> link autonegotiation and the pause autonegotiation are controlled by
> different commands.
>
> Since the ethtool -A command performs a read/modify/write of pause
> parameters, you can get strange results like these:
> # ethtool -s eth0 speed 100 duplex full autoneg off
> # ethtool -A eth0 tx off
> Cannot set device pause parameters: Invalid argument
> #
> Because, the get read pause autoneg as enabled and only the tx_pause
> member of the structure was updated.
This looks like the same argument I've been having with Heiner over
the EEE interface, except there's a difference here.
# ethtool -A eth0 autoneg on
# ethtool -s eth0 autoneg off speed 100 duplex full
After those two commands, what is the state of pause mode? The answer
is, it's disabled.
# ethtool -A eth0 autoneg off rx on tx on
is perfectly acceptable, as we are forcing pause modes at the local
end of the link.
# ethtool -A eth0 autoneg on
Now, the question is whether that should be allowed or not - but this
is merely restoring the "pause" settings that were in effect prior
to the previous command. It does not enable pause negotiation,
because autoneg as a whole is disabled, but it _allows_ pause
negotiation to occur when autoneg is enabled at some point in the
future.
Also, allowing "ethtool -A eth0 autoneg on" when "ethtool -s eth0
autoneg off" means you can configure the negotiation parameters
_before_ triggering a negotiation cycle on the link. In other words,
it would avoid:
# ethtool -s eth0 autoneg on
# # Link renegotiates
# ethtool -A eth0 autoneg on
# # Link renegotiates a second time
and it also means that if stuff has already been scripted to avoid
this, nothing breaks.
If we start rejecting ethtool -A because autoneg is disabled, then
things get difficult to configure - we would need ethtool documentation
to state that autoneg must be enabled before configuration of pause
and EEE can be done. IMHO, that hurts usability, and adds confusion.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up
next prev parent reply other threads:[~2020-05-12 18:55 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-12 0:24 [PATCH net-next 0/4] Extend phylib implementation of pause support Doug Berger
2020-05-12 0:24 ` [PATCH net-next 1/4] net: ethernet: validate pause autoneg setting Doug Berger
2020-05-12 0:47 ` Andrew Lunn
2020-05-12 18:31 ` Doug Berger
2020-05-12 18:37 ` Andrew Lunn
2020-05-12 18:55 ` Russell King - ARM Linux admin [this message]
2020-05-13 3:48 ` Doug Berger
2020-05-13 5:34 ` Russell King - ARM Linux admin
2020-05-13 9:20 ` Russell King - ARM Linux admin
2020-05-13 13:49 ` Andrew Lunn
2020-05-13 14:59 ` Michal Kubecek
2020-05-13 17:14 ` Russell King - ARM Linux admin
2020-05-13 22:09 ` Doug Berger
2020-05-13 21:31 ` Doug Berger
2020-05-13 21:27 ` Doug Berger
2020-05-12 19:08 ` Michal Kubecek
2020-05-13 2:37 ` Doug Berger
2020-05-12 3:16 ` Florian Fainelli
2020-05-12 0:24 ` [PATCH net-next 2/4] net: add autoneg parameter to linkmode_set_pause Doug Berger
2020-05-12 0:24 ` [PATCH net-next 3/4] net: ethernet: introduce phy_set_pause Doug Berger
2020-05-12 0:51 ` Andrew Lunn
2020-05-12 18:46 ` Doug Berger
2020-05-12 3:22 ` Florian Fainelli
2020-05-13 9:42 ` Russell King - ARM Linux admin
2020-05-13 21:39 ` Doug Berger
2020-05-12 0:24 ` [PATCH net-next 4/4] net: bcmgenet: add support for ethtool flow control Doug Berger
2020-05-12 3:24 ` Florian Fainelli
2020-05-13 9:52 ` Russell King - ARM Linux admin
2020-05-13 22:00 ` Doug Berger
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