Am 2020-05-10 16:52, schrieb Andrew Lunn:
More of a note to self:
Now we have three implementations, we start to see bits of common code
which could be pulled out and shared.
+static bool at803x_cdt_fault_length_valid(u16 status)
+{
+ switch (FIELD_GET(AT803X_CDT_STATUS_STAT_MASK, status)) {
+ case AT803X_CDT_STATUS_STAT_OPEN:
+ case AT803X_CDT_STATUS_STAT_SHORT:
+ return true;
+ }
+ return false;
+}
If we uses the netlink attribute values, not the PHY specific values,
this could be put in the core.
+
+static int at803x_cdt_fault_length(u16 status)
+{
+ int dt;
+
+ /* According to the datasheet the distance to the fault is
+ * DELTA_TIME * 0.824 meters.
+ *
+ * The author suspect the correct formula is:
+ *
+ * fault_distance = DELTA_TIME * (c * VF) / 125MHz / 2
+ *
+ * where c is the speed of light, VF is the velocity factor of
+ * the twisted pair cable, 125MHz the counter frequency and
+ * we need to divide by 2 because the hardware will measure the
+ * round trip time to the fault and back to the PHY.
+ *
+ * With a VF of 0.69 we get the factor 0.824 mentioned in the
+ * datasheet.
+ */
+ dt = FIELD_GET(AT803X_CDT_STATUS_DELTA_TIME_MASK, status);
+
+ return (dt * 824) / 10;
+}
There seems to be a general consensus of 0.824 meters. So we could
have helpers to convert back and forth in the core.
Yeah, but I don't know why VF is 0.69 (and it differs per cable, so
its just some kind of sensible default value). According to
https://en.wikipedia.org/wiki/Velocity_factor it should be something
around 0.64 or 0.65.
-michael
+static int at803x_cable_test_start(struct phy_device *phydev)
+{
+ /* Enable auto-negotiation, but advertise no capabilities, no link
+ * will be established. A restart of the auto-negotiation is not
+ * required, because the cable test will automatically break the
link.
+ */
+ phy_write(phydev, MII_BMCR, BMCR_ANENABLE);
+ phy_write(phydev, MII_ADVERTISE, ADVERTISE_CSMA);
+ phy_write(phydev, MII_CTRL1000, 0);
Could be a genphy_ helper.
Lets get the code merged, when we can come back and do some
refactoring.
Andrew
