On Tue, Mar 31, 2026 at 01:58:55PM +0200, Nicolai Buchwitz wrote:

On 31.3.2026 13:32, Russell King (Oracle) wrote:

quoted

On Tue, Mar 31, 2026 at 12:46:27AM +0200, Nicolai Buchwitz wrote:

quoted

Enable auto-downshift from 1000BASE-T to 100BASE-TX after 2 failed
auto-negotiation attempts by default. This ensures that links with
faulty or missing cable pairs (C and D) fall back to 100Mbps without
requiring userspace configuration.

Users can override or disable downshift at runtime:

  ethtool --set-phy-tunable eth0 downshift off

Signed-off-by: Nicolai Buchwitz <redacted>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>

I'm slightly concerned by this commit. ->config_init() is called when
the netdev attaches the PHY, and also during the resume path - and it's
the second one which I believe is a problem here.

If the user has configured the downshift, it is reasonable for the user
to expect the setting to be preserved over a suspend/resume. However,
by placing this code in ->config_init(), you will overwrite the user's
setting when the system resumes.

You have a valid point. Looking at other drivers, Marvell has the
same issue: m88e1112_config_init() unconditionally sets downshift to 3
on every config_init call.

I see two options:

1. Save the user's setting in the driver's priv struct and restore it
in config_init instead of blindly applying the default.

2. Handle it generically in the PHY core, saving/restoring tunable
state across suspend/resume for all drivers.

I'd lean towards (1) to keep this series simple. (2) could be a
follow-up that fixes Marvell and others too. What do you think?

Or (3) configure the default it in the probe function?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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