Re: [PATCH v2 net] phy: Micrel KSZ8061: link failure after cable connect

[Andrew Lunn <andrew@lunn.ch>]

On Fri, Nov 23, 2018 at 09:36:11AM +0000, Onnasch, Alexander (EXT) wrote:
> With Micrel KSZ8061 PHY, the link may occasionally not come up after
> Ethernet cable connect. The vendor's (Microchip, former Micrel) errata
> sheet 80000688A.pdf describes the problem and possible workarounds in
> detail, see below.
> The patch implements workaround 1, which permanently fixes the issue.
> 
> DESCRIPTION
> Link-up may not occur properly when the Ethernet cable is initially
> connected. This issue occurs more commonly when the cable is connected
> slowly, but it may occur any time a cable is connected. This issue occurs
> in the auto-negotiation circuit, and will not occur if auto-negotiation
> is disabled (which requires that the two link partners be set to the
> same speed and duplex).
> 
> END USER IMPLICATIONS
> When this issue occurs, link is not established. Subsequent cable
> plug/unplug cycles will not correct the issue.
> 
> WORK AROUND
> There are four approaches to work around this issue:
> 1.  This issue can be prevented by setting bit 15 in MMD device address 1,
>     register 2, prior to connecting the  cable or prior to setting the
>     Restart Auto-Negotiation bit in register 0h.The MMD registers are
>     accessed via the indirect access registers Dh and Eh, or via the Micrel
>     EthUtil utility as shown here:
>     •  If using the EthUtil utility (usually with a Micrel KSZ8061
>        Evaluation Board), type the following commands:
>        > address 1
>        > mmd 1
>        > iw 2 b61a
>     •  Alternatively, write the following registers to write to the
>        indirect MMD register:
>        Write register Dh, data 0001h
>        Write register Eh, data 0002h
>        Write register Dh, data 4001h
>        Write register Eh, data B61Ah
> 2.  The issue can be avoided by disabling auto-negotiation in the KSZ8061,
>     either by the strapping option, or by clearing bit 12 in register 0h.
>     Care must be taken to ensure that the KSZ8061 and the link partner
>     will link with the same speed and duplex. Note that the KSZ8061
>     defaults to full-duplex when auto-negotiation is off, but other
>     devices may default to half-duplex in the event of failed
>     auto-negotiation.
> 3.  The issue can be avoided by connecting the cable prior to powering-up
>     or resetting the KSZ8061, and leaving it plugged in thereafter.
> 4.  If the above measures are not taken and the problem occurs, link can
>     be recovered by setting the Restart Auto-Negotiation bit in
>     register 0h, or by resetting or power cycling the device. Reset may
>     be either hardware reset or software reset (register 0h, bit 15).
> 
> PLAN
> This errata will not be corrected in a future revision.
> 
> Signed-off-by: Alexander Onnasch <alexander.onnasch@landisgyr.com>
> Reviewed-by: Andrew Lunn <andrew@lunn.ch>
> ---

Hi Alexander

Thanks for correctly formatting the commit message, etc.

Fixes: 7ab59dc15e2f ("drivers/net/phy/micrel_phy: Add support for new PHYs")

       Andrew