Hi Maxime,

On Mon, Aug 18, 2025 at 10:15:56AM +0200, Maxime Chevallier wrote:

Hi Oleksij,

On Friday, August 15, 2025 08:35 CEST, Oleksij Rempel [off-list ref] wrote:

quoted

Implement get_mse_config() and get_mse_snapshot() for the DP83TD510E
to expose its Mean Square Error (MSE) register via the new PHY MSE
UAPI.

The DP83TD510E does not document any peak MSE values; it only exposes
a single average MSE register used internally to derive SQI. This
implementation therefore advertises only PHY_MSE_CAP_AVG, along with
LINK and channel-A selectors. Scaling is fixed to 0xFFFF, and the
refresh interval/number of symbols are estimated from 10BASE-T1L
symbol rate (7.5 MBd) and typical diagnostic intervals (~1 ms).

For 10BASE-T1L deployments, SQI is a reliable indicator of link
modulation quality once the link is established, but it does not
indicate whether autonegotiation pulses will be correctly received
in marginal conditions. MSE provides a direct measurement of slicer
error rate that can be used to evaluate if autonegotiation is likely
to succeed under a given cable length and condition. In practice,
testing such scenarios often requires forcing a fixed-link setup to
isolate MSE behaviour from the autonegotiation process.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>

[...]

quoted

+static int dp83td510_get_mse_snapshot(struct phy_device *phydev, u32 channel,
+				      struct phy_mse_snapshot *snapshot)
+{
+	int ret;
+
+	if (channel != PHY_MSE_CHANNEL_LINK &&
+	    channel != PHY_MSE_CHANNEL_A)
+		return -EOPNOTSUPP;

The doc in patch 1 says :

  > + * Link-wide mode:
  > + *  - Some PHYs only expose a link-wide aggregate MSE, or cannot map their
  > + *    measurement to a specific channel/pair (e.g. 100BASE-TX when MDI/MDI-X
  > + *    resolution is unknown). In that case, callers must use the LINK selector.

The way I understand that is that PHYs will report either channel-specific values or
link-wide values. Is that correct or are both valid ? In BaseT1 this is the same thing,
but maybe for consistency, we should report either channel values or link-wide values ?

for 100Base-T1 the LINK and channel-A selectors are effectively the
same, since the PHY only has a single channel. In this case both are
valid, and the driver will return the same answer for either request.

I decided to expose both for consistency:
- on one side, the driver already reports pair_A information for the
  cable test, so it makes sense to allow channel-A here as well;
- on the other side, if a caller such as a generic link-status/health
  request asks for LINK, we can also provide that without special
  casing.

So the driver just answers what it can. For this PHY, LINK and
channel-A map to the same hardware register, and all other selectors
return -EOPNOTSUPP.

Best regards,
Oleksij
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