netdev - Re: [PATCH net-next v1 1/1] net: phy: dp83td510: Add basic support for the DP83TD510 Ethernet PHY

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Date:   Mon, 26 Jul 2021 14:18:51 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        Dan Murphy <dmurphy@...com>, kernel@...gutronix.de,
        David Jander <david@...tonic.nl>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net-next v1 1/1] net: phy: dp83td510: Add basic support
 for the DP83TD510 Ethernet PHY

Hi Andrew,

On Fri, Jul 23, 2021 at 08:12:05PM +0200, Andrew Lunn wrote:
> On Fri, Jul 23, 2021 at 07:08:49PM +0200, Oleksij Rempel wrote:
> > Hi Andrew,
> > 
> > On Fri, Jul 23, 2021 at 03:22:16PM +0200, Andrew Lunn wrote:
> > > On Fri, Jul 23, 2021 at 12:42:18PM +0200, Oleksij Rempel wrote:
> > > > The DP83TD510E is an ultra-low power Ethernet physical layer transceiver
> > > > that supports 10M single pair cable.
> > > > 
> > > > This driver provides basic support for this chip:
> > > > - link status
> > > > - autoneg can be turned off
> > > > - master/slave can be configured to be able to work without autoneg
> > > > 
> > > > This driver and PHY was tested with ASIX AX88772B USB Ethernet controller.
> > > 
> > > Hi Oleksij
> > > 
> > > There were patches flying around recently for another T1L PHY which
> > > added new link modes. Please could you work together with that patch
> > > to set the phydev features correctly to indicate this PHY is also a
> > > T1L, and if it support 2.4v etc.
> > 
> > ACK, thx. I was not able to spend enough time to investigate all needed
> > caps, so I decided to go mainline with limited functionality first.
> 
> Limited functionality is fine, but what is implemented should be
> correct. And from what i see in the patch, it is hard to know if the
> PHYs basic features are correctly determined. What does ethtool show?
> Is 100BaseT being offered? Half duplex?

With current driver ethtool with show this information:
Settings for eth1:
	Supported ports: [ TP	 MII ]
	Supported link modes:   Not reported
	Supported pause frame use: Symmetric Receive-only
	Supports auto-negotiation: Yes
	Supported FEC modes: Not reported
	Advertised link modes:  Not reported
	Advertised pause frame use: No
	Advertised auto-negotiation: Yes
	Advertised FEC modes: Not reported
	Speed: 10Mb/s
	Duplex: Full
	Auto-negotiation: on
	master-slave cfg: unknown
	master-slave status: unknown
	Port: Twisted Pair
	PHYAD: 1
	Transceiver: external
	MDI-X: Unknown
	Supports Wake-on: pg
	Wake-on: p
        Current message level: 0x00000007 (7)
                               drv probe link
	Link detected: yes

> > voltage depends on the end application: cable length, safety requirements. I do
> > not see how this can be chosen only on auto negotiation. We would need proper
> > user space interface to let user/integrator set the limits.
> 
> I think we are talking at cross purposes here. As far as i understand
> T1L supports the data signals to be 2.4Vpp as well as the usual
> 1Vpp. This is something which can be negotiated in the same way as
> master/slave, duplex etc.
> 
> I suspect you are talking about the PoE aspects. That is outside the
> scope for phylib. PoE in general is not really supported in the Linux
> kernel, and probably needs a subsystem of its own.

No, no. I'm talking about data signals configuration (2.4Vpp/1Vpp), which
depends on application and cable length. 1Vpp should not be used with
cable over 200 meter and 2.4Vpp should not be used on safety critical
applications. 

Regards,
Oleksij
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