net: pcs: xpcs: fix SGMII state reading

Commit 2a22b7ae2fa3 ("net: pcs: xpcs: adapt Wangxun NICs for SGMII mode")
added a path in xpcs_get_state_c37_sgmii() that reads speed/duplex from
BMCR after AN completes. However, BMCR does not reflect the negotiated
result on the hardware where this has been tested:

- On RK3568 (MAC side SGMII), BMCR returns a fixed hardware reset value
- Wangxun engineer Jiawen Wu confirmed that on their side, "BMCR looks
  like it only wants to be return as 0" [0]

The correct information is available in CL37_ANSGM_STS, which contains
the actual link status and negotiated speed/duplex.

This bug was previously masked by phylink core, which overrides the PCS
link state with the PHY state when a PHY is present:

        /* If we have a phy, the "up" state is the union of both the
         * PHY and the MAC
         */
        if (phy)
                link_state.link &= pl->phy_state.link;

Thus, when the link is down, the PHY's link_down state is applied on top
of whatever the PCS reports, hiding the broken PCS state reading path.

Modify xpcs_get_state_c37_sgmii() to:
1. Read link state from CL37_ANSGM_STS
2. If link is up, report speed/duplex from CL37_ANSGM_STS
3. Remove the broken BMCR reading path entirely

Also properly set state->an_complete to reflect the AN completion status,
and clear CL37_ANCMPLT_INTR when link is down to avoid stale state.

[0] https://lore.kernel.org/all/000c01dd1593$2ac0b0f0$804212d0$@trustnetic.com/

Fixes: 2a22b7ae2fa3 ("net: pcs: xpcs: adapt Wangxun NICs for SGMII mode")
Cc: stable@vger.kernel.org
Tested-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: Coia Prant <coiaprant@gmail.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260717074324.3250043-2-coiaprant@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions