netdev - RE: [PATCH] net: phy: realtek: Add dummy stubs for MMD register access for rtl8211b

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Date:   Mon, 19 Mar 2018 14:31:19 +0000
From:   Claudiu Manoil <claudiu.manoil@....com>
To:     Andrew Lunn <andrew@...n.ch>, Kevin Hao <haokexin@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: RE: [PATCH] net: phy: realtek: Add dummy stubs for MMD register
 access for rtl8211b

> -----Original Message-----
> From: Andrew Lunn [mailto:andrew@...n.ch]
> Sent: Monday, March 19, 2018 2:40 PM
> To: Kevin Hao <haokexin@...il.com>
> Cc: netdev@...r.kernel.org; Florian Fainelli <f.fainelli@...il.com>; Claudiu
> Manoil <claudiu.manoil@....com>
> Subject: Re: [PATCH] net: phy: realtek: Add dummy stubs for MMD register
> access for rtl8211b
> 
> On Mon, Mar 19, 2018 at 08:05:47PM +0800, Kevin Hao wrote:
> > The Ethernet on mpc8315erdb is broken since commit b6b5e8a69118
> > ("gianfar: Disable EEE autoneg by default"). The reason is that even
> > though the rtl8211b doesn't support the MMD extended registers access,
> > it does return some random values if we trying to access the MMD
> > register via indirect method. This makes it seem that the EEE is
> > supported by this phy device. And the subsequent writing to the MMD
> > registers does cause the phy malfunction. So add dummy stubs for the
> > MMD register access to fix this issue.
> 
> Hi Kevin
> 
> The Micrel PHY has the same problem. Please add generic
> genphy_read_mmd_unsupported() and
> genphy_write_mmd_unsupported() to phy_device.c, and use them from
> both the Micrel and Realtek PHY drivers.
> 
> Also, a return value of -EOPNOTSUPP is more appropriate.
> 

This gianfar patch should have been a temporary workaround.
Obviously, the driver of an (old) eth controller that does not support EEE should
not be modified to have the same eth controller work normally when some new EEE
capable phy happens to be attached to that controller (i.e. on a new board).
It should be up to the phy integration layer to identify that the controller and the phy
are not EEE compatible, and restrict the phy from entering EEE mode. (without any
change to the eth driver)

Claudiu