linux-kernel - Re: [PATCH net-next v1 1/1] net: phy: dp83td510: add cable testing support

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Message-ID: <ZpE_WwtSSdxGyWtC@pengutronix.de>
Date: Fri, 12 Jul 2024 16:36:11 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andrew Lunn <andrew@...n.ch>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	kernel@...gutronix.de, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next v1 1/1] net: phy: dp83td510: add cable testing
 support

Hi Andrew,

On Mon, Jul 08, 2024 at 06:44:22PM +0200, Andrew Lunn wrote:
> On Mon, Jul 08, 2024 at 04:05:42PM +0200, Oleksij Rempel wrote:
> > Implement the TDR test procedure as described in "Application Note
> > DP83TD510E Cable Diagnostics Toolkit revC", section 3.2.
> > 
> > The procedure was tested with "draka 08 signalkabel 2x0.8mm". The reported
> > cable length was 5 meters more for each 20 meters of actual cable length.
> > For instance, a 20-meter cable showed as 25 meters, and a 40-meter cable
> > showed as 50 meters. Since other parts of the diagnostics provided by this
> > PHY (e.g., Active Link Cable Diagnostics) require accurate cable
> > characterization to provide proper results, this tuning can be implemented
> > in a separate patch/interface.
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > ---
> >  drivers/net/phy/dp83td510.c | 158 ++++++++++++++++++++++++++++++++++++
> >  1 file changed, 158 insertions(+)
> > 
> > diff --git a/drivers/net/phy/dp83td510.c b/drivers/net/phy/dp83td510.c
> > index d7616b13c5946..3375fa82927d0 100644
> > --- a/drivers/net/phy/dp83td510.c
> > +++ b/drivers/net/phy/dp83td510.c
> > @@ -4,6 +4,7 @@
> >   */
> >  
> >  #include <linux/bitfield.h>
> > +#include <linux/ethtool_netlink.h>
> >  #include <linux/kernel.h>
> >  #include <linux/module.h>
> >  #include <linux/phy.h>
> > @@ -29,6 +30,42 @@
> >  #define DP83TD510E_INT1_LINK			BIT(13)
> >  #define DP83TD510E_INT1_LINK_EN			BIT(5)
> >  
> > +#define DP83TD510E_TDR_CFG			0x1e
> > +#define DP83TD510E_TDR_START			BIT(15)
> > +#define DP83TD510E_TDR_DONE			BIT(1)
> > +#define DP83TD510E_TDR_FAIL			BIT(0)
> > +
> > +#define DP83TD510E_CTRL				0x1f
> > +#define DP83TD510E_CTRL_HW_RESET		BIT(15)
> > +#define DP83TD510E_CTRL_SW_RESET		BIT(14)
> > +
> > +#define DP83TD510E_TDR_CFG1			0x300
> 
> > +/* TX_TYPE: Transmit voltage level for TDR. 0 = 1V, 1 = 2.4V */
> > +#define DP83TD510E_TDR_TX_TYPE			BIT(12)
> 
> This does not appear to be used, so it is not too important. But i
> generally encode this as
> 
> #define DP83TD510E_TDR_TX_TYPE_1V		(0 << 12)
> #define DP83TD510E_TDR_TX_TYPE_2V4		(1 << 12)
> 
> You can then OR in DP83TD510E_TDR_TX_TYPE_1V which does nothing, but
> does document you are using 1V for the test.

Ack.

> > +#define DP83TD510E_TDR_CFG2			0x301
> > +#define DP83TD510E_TDR_END_TAP_INDEX_1		GENMASK(14, 8)
> > +#define DP83TD510E_TDR_END_TAP_INDEX_1_DEF	36
> > +#define DP83TD510E_TDR_START_TAP_INDEX_1	GENMASK(6, 0)
> > +#define DP83TD510E_TDR_START_TAP_INDEX_1_DEF	3
> 
> Does this correspond the minimum and maximum distance it will test?
> Is this 3m to 36m?

No. At least, i can't confirm it with tests.

If I see it correctly, this PHY is using SSTDR instead of usual TDR.
Instead of pulses it will send modulated transmission with default
length of 16ms

I tried my best google foo, but was not able to find anything
understandable about "Start/End tap index for echo coeff sweep for segment 1"
im context of SSTDR. If anyone know more about this, please tell me :)

Regards,
Oleksij
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