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[2003:ea:8f47:db00:69f9:84c:2cc6:baef]) by smtp.googlemail.com with ESMTPSA id j16sm14216835wrp.62.2019.08.19.12.07.26 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 19 Aug 2019 12:07:26 -0700 (PDT) Subject: Re: [PATCH net-next 0/1] Add BASE-T1 PHY support To: Christian Herber , "davem@davemloft.net" Cc: "netdev@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <20190815153209.21529-1-christian.herber@nxp.com> <8c15b855-6947-9930-c3df-71a64fbff33b@gmail.com> From: Heiner Kallweit Message-ID: <13e65051-fe4f-5964-30b3-75285e6d2eee@gmail.com> Date: Mon, 19 Aug 2019 21:07:22 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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