The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 80d4609008e6d696a279e39ae7458c916fcd44c1 Mon Sep 17 00:00:00 2001 From: Yannick Vignon yannick.vignon@nxp.com Date: Thu, 3 Feb 2022 17:00:25 +0100 Subject: [PATCH] net: stmmac: ensure PTP time register reads are consistent

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: 92ba6888510c ("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

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c index 074e2cdfb0fa..a7ec9f4d46ce 100644 --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c @@ -145,15 +145,20 @@ static int adjust_systime(void __iomem *ioaddr, u32 sec, u32 nsec,

static void get_systime(void __iomem *ioaddr, u64 *systime) { - u64 ns; - - /* 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; + u64 ns, sec0, sec1; + + /* Get the TSS value */ + sec1 = readl_relaxed(ioaddr + PTP_STSR); + do { + sec0 = sec1; + /* Get the TSSS value */ + 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); }

static void get_ptptime(void __iomem *ptpaddr, u64 *ptp_time)