Re: [PATCH net-next] net: ethtool: allow MAC drivers to override ethtool get_ts_info

On Thu, Jan 14, 2021 at 05:31:11PM +0000, Russell King - ARM Linux admin wrote:

On Thu, Jan 14, 2021 at 09:27:12AM -0800, Richard Cochran wrote:

quoted

Thanks for the reminder.  We ended up with having to review the MAC
drivers that support phydev.

   https://lore.kernel.org/netdev/20200730194427.GE1551@shell.armlinux.org.uk/ (local)

There is at least the FEC that supports phydev.  I have a board that
combines the FEC with the dp83640 PHYTER, and your patch would break
this setup.  (In the case of this HW combination, the PHYTER is
superior in every way.)

Another combination that I have seen twice is the TI am335x with its
cpsw MAC and the PHYTER.  Unfortunately I don't have one of these
boards, but people made them because the cpsw MAC supports time
stamping in a way that is inadequate.

I *think* the cpsw/phyter combination would work with your patch, but
only if the users disable CONFIG_TI_CPTS at compile time.

I think then the only solution is to move the decision how to handle
get_ts_info into each MAC driver and get rid of:

	if (phy_has_tsinfo(phydev))
	        return phy_ts_info(phydev, info);

in __ethtool_get_ts_info().

Thinking about this more, that is an impossible task - there's no
obvious information around to suggest which ethernet drivers could
possibly be attached to a phylib PHY that supports PTP.

So, I think the only way to prevent a regression with the code as
it is today is that we _never_ support PTP on Marvell PHYs - because
doing so _will_ break the existing MVPP2 driver's implementation and
cause a regression.

Right now, there is no option: if a PHY supports PTP, then the only
option is to use the PHYs PTP. Which is utterly rediculous.

Unless you can see a way around it. Because I can't.

-- 
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