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net: phy: smsc: Disable Energy Detect Power-Down in interrupt mode

Ghost User requested to merge github/fork/l1k/smsc_edpd_fix into revpi-5.10

Created by: l1k

Simon reports that if two LAN9514 USB adapters are directly connected without an intermediate switch, the link fails to come up and link LEDs remain dark. The issue was introduced by commit 1ce8b372 ("usbnet: smsc95xx: Forward PHY interrupts to PHY driver to avoid polling").

The PHY suffers from a known erratum wherein link detection becomes unreliable if Energy Detect Power-Down is used. In poll mode, the driver works around the erratum by briefly disabling EDPD for 640 msec to detect a neighbor, then re-enabling it to save power.

In interrupt mode, no interrupt is signaled if EDPD is used by both link partners, so it must not be enabled at all.

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