netdev - Re: [PATCH net-next] net: phy: let genphy_c45_read

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Date:   Thu, 7 Feb 2019 21:21:23 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        Russell King <linux@...linux.org.uk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: let genphy_c45_read_link manage the
 devices to check

On 07.02.2019 20:57, Andrew Lunn wrote:
> On Thu, Feb 07, 2019 at 08:05:55PM +0100, Heiner Kallweit wrote:
>> Let genphy_c45_read_link manage the devices to check, this removes
>> overhead from callers. Devices VEND1 and VEND2 will never be checked,
>> for now adopt the logic of the Marvell driver to also exclude PHY XS.
>>
>> At the moment we have very few clause 45 PHY drivers, so we are
>> lacking experience whether other drivers will have to exclude further
>> devices, or may need to check PHY XS. If we should figure out that
>> list of devices to check needs to be configurable, I think best will
>> be to add a device list member to struct phy_driver.
> 
> Hi Heiner
> 
> For the Aquantia PHY you probably need to exclude MDIO_MMD_C22EXT.
> 
> There is no register 1D:1 listed in the datasheet.
> 
Thanks, Andrew. Right, the Aquantia PHY doesn't seem to have the C22EXT
MMD. Because the Aquantia PHY has no device 29 in its package the code
should work.
I also checked the 802.3 spec and it says that registers 29.0 to
29.4 are reserved. At another location the 802.3 spec states that read
access to non-existing registers should return a zero value.
Therefore current code (when reading a 0 from 29.1) may come to the
false conclusion that device 29 reports link down.
So it seems we have to exclude device C22EXT in general. I'll add that
and submit a v2.

> PHY XS is the interface towards the MAC. You cannot configure the MAC
> to use the correct interface mode until the PHY has link to its peer
> and the link mode has been determined. So you need the PHY to signal
> link up independent of the MAC-PHY link, to kick off the configuration
> of the MAC. When using phylink, the MAC can indicate it has a link to
> the PHY using phylink_mac_change().
> 
OK, so excluding PHY XS is right.

>       Andrew
>  
> 
Heiner