Message-ID: <AM6PR0402MB3798FCBF1EE592687B13A3C386AB0@AM6PR0402MB3798.eurprd04.prod.outlook.com>
Date:   Tue, 20 Aug 2019 13:36:09 +0000
From:   Christian Herber <christian.herber@....com>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [EXT] Re: [PATCH net-next 0/1] Add BASE-T1 PHY support

On 19.08.2019 21:07, Heiner Kallweit wrote:
> Caution: EXT Email
> 
> On 19.08.2019 08:32, Christian Herber wrote:
>> On 16.08.2019 22:59, Heiner Kallweit wrote:
>>> On 15.08.2019 17:32, Christian Herber wrote:
>>>> This patch adds basic support for BASE-T1 PHYs in the framework.
>>>> BASE-T1 PHYs main area of application are automotive and industrial.
>>>> BASE-T1 is standardized in IEEE 802.3, namely
>>>> - IEEE 802.3bw: 100BASE-T1
>>>> - IEEE 802.3bp 1000BASE-T1
>>>> - IEEE 802.3cg: 10BASE-T1L and 10BASE-T1S
>>>>
>>>> There are no products which contain BASE-T1 and consumer type PHYs like
>>>> 1000BASE-T. However, devices exist which combine 100BASE-T1 and 1000BASE-T1
>>>> PHYs with auto-negotiation.
>>>
>>> Is this meant in a way that *currently* there are no PHY's combining Base-T1
>>> with normal Base-T modes? Or are there reasons why this isn't possible in
>>> general? I'm asking because we have PHY's combining copper and fiber, and e.g.
>>> the mentioned Aquantia PHY that combines NBase-T with 1000Base-T2.
>>>
>>>>
>>>> The intention of this patch is to make use of the existing Clause 45 functions.
>>>> BASE-T1 adds some additional registers e.g. for aneg control, which follow a
>>>> similiar register layout as the existing devices. The bits which are used in
>>>> BASE-T1 specific registers are the same as in basic registers, thus the
>>>> existing functions can be resued, with get_aneg_ctrl() selecting the correct
>>>> register address.
>>>>
>>> If Base-T1 can't be combined with other modes then at a first glance I see no
>>> benefit in defining new registers e.g. for aneg control, and the standard ones
>>> are unused. Why not using the standard registers? Can you shed some light on that?
>>>
>>> Are the new registers internally shadowed to the standard location?
>>> That's something I've seen on other PHY's: one register appears in different
>>> places in different devices.
>>>
>>>> The current version of ethtool has been prepared for 100/1000BASE-T1 and works
>>>> with this patch. 10BASE-T1 needs to be added to ethtool.
>>>>
>>>> Christian Herber (1):
>>>>     Added BASE-T1 PHY support to PHY Subsystem
>>>>
>>>>    drivers/net/phy/phy-c45.c    | 113 +++++++++++++++++++++++++++++++----
>>>>    drivers/net/phy/phy-core.c   |   4 +-
>>>>    include/uapi/linux/ethtool.h |   2 +
>>>>    include/uapi/linux/mdio.h    |  21 +++++++
>>>>    4 files changed, 129 insertions(+), 11 deletions(-)
>>>>
>>>
>>> Heiner
>>>
>>
>> Hi Heiner,
>>
>> I do not think the Aquantia part you are describing is publicly
>> documented, so i cannot comment on that part.
> Right, datasheet isn't publicly available. All I wanted to say with
> mentioning this PHY: It's not a rare exception that a PHY combines
> standard BaseT modes with "non-consumer" modes for special purposes.
> One practical use case of this proprietary 1000Base-T2 mode is
> re-using existing 2-pair cabling in aircrafts.
> 
>> There are multiple reasons why e.g. xBASE-T1 plus 1000BASE-T is
>> unlikely. First, the is no use-case known to me, where this would be
>> required. Second, there is no way that you can do an auto-negotiation
>> between the two, as these both have their own auto-neg defined (Clause
>> 28/73 vs. Clause 98). Thirdly, if you would ever have a product with
>> both, I believe it would just include two full PHYs and a way to select
>> which flavor you want. Of course, this is the theory until proven
>> otherwise, but to me it is sufficient to use a single driver.
>>
> I'm with you if you say it's unlikely. However your statement in the
> commit message leaves the impression that there can't be such a device.
> And that's a difference.
> 
> Regarding "including two full PHYs":
> This case we have already, there are PHYs combining different IP blocks,
> each one supporting a specific mode (e.g. copper and fiber). There you
> also have the case of different autoneg methods, clause 28 vs. clause 37.
> 
>> The registers are different in the fields they include. It is just that
>> the flags which are used by the Linux driver, like restarting auto-neg,
>> are at the same position.
>>
> Good to know. Your commit description doesn't mention any specific PHY.
> I suppose you have PHYs you'd like to operate with the genphy_c45 driver.
> Could you give an example? And ideally, is a public datasheet available?
> 
>> Christian
>>
>>
> Heiner
> 

There are no public BASE-T1 devices on the market right now that use 
Clause 45 standard registers. The first such products were developed 
before the IEEE standard (BroadR-Reach) and used Clause 22 access (see 
e.g. the support in the Kernel for TJA110x).

The most convenient way to test with a BASE-T1 device would be to use an 
SFP (e.g. 
https://technica-engineering.de/produkt/1000base-t1-sfp-module/). 
Alternative source could be Goepel.

There are also a number of media-converters around where one could break 
out the MDIO and connect to a processor. Of course, in all cases it 
should be made sure that this is a Clause-45 device.

As all relevant parts are NDA-restricted, this is pretty much all the 
information I can share.

Christian

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