linux-kernel - ptp device strangeness

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Date:   Fri, 01 Sep 2017 17:28:34 +0200
From:   Tim Sander <tim@...eglstein.org>
To:     Richard Cochran <richardcochran@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     netdev@...r.kernel.org
Subject: ptp device strangeness

Hi

I am currently using ptp on a Altera/Intel SOC with a dp8640 PHY.
PTP functionality seems to be right. But i am doing timestamping
with gpio0 and sometimes i loose the sync of the stamping and
the events. So i would like to read out all messages. Reading O_NONBLOCK
does not work so i tried polling from usermode with the below code:

		np = poll(&ev, 1, 0);
		ev.fd=ptpDev;
		ev.events = POLLIN;
		if (np>0) {
			if (ev.revents>0) {
				std::cout<<"discarded ptp event"<<std::endl;
				read(ptpDev, &event, sizeof(event));
			}
But as confirmed in the debugger np=1 and read blocks forever.
I don't think that this is correct behavior?

For pinning down this misbehavior I would like to know it this is a local 
problem of my hardware or if this is a general problem with the ptp chardev 
interface? 

I am currently on 4.11.12. As this is the latest preempt rt release.

Best regards
Tim