On Wed, Feb 26, 2020 at 12:08:17AM +0100, Michael Walle wrote:

This patchset is the current state of my work for adding PHY timestamping
support. I just wanted to post this to the mailinglist before I never do
it. Maybe its a starting point for other people. That being said, I
wouldn't mind comments ;) The code basically works but there are three
major caveats:

 (1) The reading of timestamps via MDIO sometimes return wrong values. What
     I see is that a part of the timestamp corresponds to the new timestamp
	 while another part still contains old values. Thus at the moment, I'm
	 reading the registers twice. I don't know if the reading actually
	 affects the update of the timestamp or the different timing (my MDIO
	 bus is rather slow, so reading the timestamp a second time take some
	 amount of time; but I've also tested with some delays and it didn't
	 had any effects). There is also no possibility to read the timestamp
	 atomically :(

Hi Michael

That sounds fundamentally broken. Which would be odd. Sometimes there
is a way to take a snapshot of the value. Reading the first word could
trigger this snapshot. Or the last word, or some status register. One
would hope the datasheet would talk about this.

      Andrew