Merge branch 'net-stmmac-increase-clk_ptp_ref-rate'

Merge branch 'net-stmmac-increase-clk_ptp_ref-rate'

Andrew Halaney says:

====================
net: stmmac: Increase clk_ptp_ref rate

This series aims to increase the clk_ptp_ref rate to get the best
possible PTP timestamping resolution possible. Some modified disclosure
about my development/testing process from the RFC/RFT v1 follows.

Disclosure: I don't know much about PTP beyond what you can google in an
afternoon, don't have access to documentation about the stmmac IP,
and have only tested that (based on code comments and git commit
history) the programming of the subsecond register (and the clock rate)
makes more sense with these changes. Qualcomm has tested a similar
change offlist, verifying PTP more formally as I understand it.

The last version was an RFC/RFT, but I didn't get a lot of confirmation
that doing patch 3 in that series (essentially setting clk_ptp_ref to
whatever its max value is) for the whole stmmac ecosystem was a safe
idea. So I am erring on the side of caution and doing this for the
Qualcomm platform only. See v1 for an approach that would apply to
all stmmac platform drivers with clk_ptp_ref.

v1: https://lore.kernel.org/netdev/20230711205732.364954-1-ahalaney@redhat.com/
====================

Link: https://lore.kernel.org/r/20230725211853.895832-2-ahalaney@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>