netdev - Re: [PATCH 1/1] net: core: 'ethtool' issue with querying phy settings

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Message-Id: <20150531.171940.1635713770956335110.davem@davemloft.net>
Date:	Sun, 31 May 2015 17:19:40 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ben@...adent.org.uk
Cc:	aparames@...adcom.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	bcm-kernel-feedback-list@...adcom.com, rjui@...adcom.com,
	sbranden@...adcom.com, jdzheng@...adcom.com
Subject: Re: [PATCH 1/1] net: core: 'ethtool' issue with querying phy
 settings

From: Ben Hutchings <ben@...adent.org.uk>
Date: Sun, 31 May 2015 20:54:06 +0100

> On Fri, 2015-05-22 at 16:15 -0400, David Miller wrote:
>> From: Arun Parameswaran <aparames@...adcom.com>
>> Date: Wed, 20 May 2015 14:35:30 -0700
>> 
>> > When trying to configure the settings for PHY1, using commands
>> > like 'ethtool -s eth0 phyad 1 speed 100', the 'ethtool' seems to
>> > modify other settings apart from the speed of the PHY1, in the
>> > above case.
>> > 
>> > The ethtool seems to query the settings for PHY0, and use this
>> > as the base to apply the new settings to the PHY1. This is
>> > causing the other settings of the PHY 1 to be wrongly
>> > configured.
>> > 
>> > The issue is caused by the '_ethtool_get_settings()' API, which
>> > gets called because of the 'ETHTOOL_GSET' command, is clearing
>> > the 'cmd' pointer (of type 'struct ethtool_cmd') by calling
>> > memset. This clears all the parameters (if any) passed for the
>> > 'ETHTOOL_GSET' cmd. So the driver's callback is always invoked
>> > with 'cmd->phy_address' as '0'.
>> > 
>> > The '_ethtool_get_settings()' is called from other files in the
>> > 'net/core'. So the fix is applied to the 'ethtool_get_settings()'
>> > which is only called in the context of the 'ethtool'.
>> > 
>> > Signed-off-by: Arun Parameswaran <aparames@...adcom.com>
>> > Reviewed-by: Ray Jui <rjui@...adcom.com>
>> > Reviewed-by: Scott Branden <sbranden@...adcom.com>
>> 
>> Applied and queued up for -stable, thanks.
> 
> Please revert this.  This is an incompatible API change, not a bug fix.
> The established semantics are that 'phyad' is filled in by the driver;
> it is not a parameter to the ETHTOOL_GSET command.

But then how in the world can the user specify specific PHY ADs for
a device that will respond to more than one?
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