RE: [PATCH 2/3] net: macb: add support for C45 MDIO read/write

[Milind Parab <mparab@cadence.com>]

>-----Original Message-----
>From: Andrew Lunn <andrew@lunn.ch>
>Sent: Thursday, November 28, 2019 12:21 AM
>To: Nicolas.Ferre@microchip.com
>Cc: Milind Parab <mparab@cadence.com>; antoine.tenart@bootlin.com;
>davem@davemloft.net; netdev@vger.kernel.org; f.fainelli@gmail.com;
>hkallweit1@gmail.com; linux-kernel@vger.kernel.org; Dhananjay Vilasrao
>Kangude <dkangude@cadence.com>; Parshuram Raju Thombare
><pthombar@cadence.com>; rmk+kernel@arm.linux.org.uk
>Subject: Re: [PATCH 2/3] net: macb: add support for C45 MDIO read/write
>
>EXTERNAL MAIL
>
>
>On Wed, Nov 27, 2019 at 06:31:54PM +0000, Nicolas.Ferre@microchip.com
>wrote:
>> On 26/11/2019 at 15:37, Andrew Lunn wrote:
>> > On Tue, Nov 26, 2019 at 09:09:49AM +0000, Milind Parab wrote:
>> >> This patch modify MDIO read/write functions to support
>> >> communication with C45 PHY.
>> >
>> > I think i've asked this before, at least once, but you have not
>> > added it to the commit messages. Do all generations of the macb support
>C45?
>>
>> For what I can tell from the different IP revisions that we
>> implemented throughout the years in Atmel then Microchip products
>> (back to
>> at91rm9200 and at91sam9263), it seems yes.
>>
>> The "PHY Maintenance Register" "MACB_MAN_*" was always present with
>> the same bits 32-28 layout (with somehow different names).
>>
>> But definitively we would need to hear that from Cadence itself which
>> would be far better.
>
>Hi Nicolas
>
>Thanks, that is useful.
>
>I'm just trying to avoid backward compatibility issues, somebody issues a C45
>request on old silicon and it all goes horribly wrong.

This patch doesn't affect current C22 operation of the driver. 
However if a user selects C45 on incompatible MAC (there are old MAC, prior to Release1p10, released 10th April 2003) MDIO operations may fails.
Adding check will cover this corner case.

We will add this check in v2 of patch set.
>
>       Andrew