Re: [PATCH net-next v3 3/3] phy: dp83td510: Utilize ALCD for cable length measurement when link is active

[Andrew Lunn]

On Thu, Aug 22, 2024 at 02:07:03PM +0200, Oleksij Rempel wrote:
> In industrial environments where 10BaseT1L PHYs are replacing existing
> field bus systems like CAN, it's often essential to retain the existing
> cable infrastructure. After installation, collecting metrics such as
> cable length is crucial for assessing the quality of the infrastructure.
> Traditionally, TDR (Time Domain Reflectometry) is used for this purpose.
> However, TDR requires interrupting the link, and if the link partner
> remains active, the TDR measurement will fail.
> 
> Unlike multi-pair systems, where TDR can be attempted during the MDI-X
> switching window, 10BaseT1L systems face greater challenges. The TDR
> sequence on 10BaseT1L is longer and coincides with uninterrupted
> autonegotiation pulses, making TDR impossible when the link partner is
> active.
> 
> The DP83TD510 PHY provides an alternative through ALCD (Active Link
> Cable Diagnostics), which allows for cable length measurement without
> disrupting an active link. Since a live link indicates no short or open
> cable states, ALCD can be used effectively to gather cable length
> information.
> 
> Enhance the dp83td510 driver by:
> - Leveraging ALCD to measure cable length when the link is active.
> - Bypassing TDR when a link is detected, as ALCD provides the required
>   information without disruption.
> 
> Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>

Reviewed-by: Andrew Lunn <andrew@xxxxxxx>

    Andrew