Commit 4a674b8e authored Feb 03, 2022 by Yannick Vignon Committed by Greg Kroah-Hartman Feb 08, 2022

net: stmmac: ensure PTP time register reads are consistent

commit 80d4609008e6d696a279e39ae7458c916fcd44c1 upstream.

Even if protected from preemption and interrupts, a small time window
remains when the 2 register reads could return inconsistent values,
each time the "seconds" register changes. This could lead to an about
1-second error in the reported time.

Add logic to ensure the "seconds" and "nanoseconds" values are consistent.

Fixes: 92ba6888 ("stmmac: add the support for PTP hw clock driver")
Signed-off-by: Yannick Vignon <yannick.vignon@nxp.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/20220203160025.750632-1-yannick.vignon@oss.nxp.com

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 9afc0286

drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c

+12 −7

Original line number	Diff line number	Diff line
		@@ -149,15 +149,20 @@ static int adjust_systime(void __iomem *ioaddr, u32 sec, u32 nsec,

		static void get_systime(void __iomem ioaddr, u64 systime)
		{
		u64 ns;
		u64 ns, sec0, sec1;

		/* Get the TSS value */
		sec1 = readl_relaxed(ioaddr + PTP_STSR);
		do {
		sec0 = sec1;
		/* Get the TSSS value */
		ns = readl(ioaddr + PTP_STNSR);
		/* Get the TSS and convert sec time value to nanosecond */
		ns += readl(ioaddr + PTP_STSR) * 1000000000ULL;
		ns = readl_relaxed(ioaddr + PTP_STNSR);
		/* Get the TSS value */
		sec1 = readl_relaxed(ioaddr + PTP_STSR);
		} while (sec0 != sec1);

		if (systime)
		*systime = ns;
		systime = ns + (sec1 1000000000ULL);
		}

		const struct stmmac_hwtimestamp stmmac_ptp = {