On Tue, Jan 07, 2025 at 01:16:33PM +0000, Daniel Golle wrote:

On Tue, Jan 07, 2025 at 12:47:14PM +0000, Russell King (Oracle) wrote:

quoted

... but we don't see link-up reported by the PCS after the PHY comes
up. Why is that - I think that needs investigation before we proceed
to patch the issue, because that suggests the PCS isn't seeing
valid 2500base-X from the PHY.

The PCS doesn't support in-band status in 2500Base-X mode, or at least
the implementation isn't compatible with those RealTek PHYs.

There is in-band for base-X, which involves 16-bit control words to
report the capabilities of either end (basically half/full duplex,
pause modes). Unlike SGMII, it doesn't contain any status bits for
link up, because that is irrelevant.

Link-up state in base-X modes comes from the PCS itself, whether the
PCS is in sync with the media, and whether it has valid format. This
has *nothing* to do with in-band.

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