netdev - Re: [PATCH] net: phy: Add TJA1100 BroadR-Reach PHY driver.

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Date:   Sat, 9 Jun 2018 10:08:17 +0300
From:   Kirill Kranke <kranke.kirill@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH] net: phy: Add TJA1100 BroadR-Reach PHY driver.

Hi Andrew.

Thanks for your comments. I will update the patch a bit later.

>
> Does 100Base-T1/cause 96 define a way to identify a PHY which
> implements this? I'm just wondering if we can do this in the generic
> code, for devices which correctly implement the standard?
>

Well, I did research IEEE 802.3 standards before implementing the
Patch. Initially I
wanted to update generic phy driver. I did not find a way to identify
100Base-T1 PHY
using Clause 22 MDIO. This section is completely missing at IEEE 802.3bw, which
describe 100Base-T1.

There are some updates to Clause 45 registers at IEEE 802.3bw. They add
"BASE-T1 PMA/PMD extended ability" to PMA/PMD registers.

At Clause 96 they state following: "The MDIO capability described in Clause 45
defines several variables that provide control and status information for and
about the PMA and PCS."

In the same time I have played with a two different 100Base-T1 PHYs. Both
use different Clause 22 registers to advertise their abilities, both
are incompatible.
None use Clause 45 for this purpose.

It seems that this is going to be 100Base-T1 mess while IEEE 802.3bw
miss Clause 22 updates. Clause 45 is rarely used from my experience. Probably
IEEE expected 100Base-T1 PHYs to go for Clause 45 MDIO and this did not work
so far.

>
> This is the second T1 driver we have had recently. It might make sense to add a
> PHY_T1_FEATURES macro the include/linux/phy.h
>

This seems reasonable, indeed.

>
> Don't you also want SUPPORTED_TP?
>

True, I will add SUPPORTED_TP in next revision of the Patch.

Kirill