[PATCH 5.16 077/126] net: stmmac: ensure PTP time register reads are consistent

Greg Kroah-Hartman
2022-02-07T11:59:03Z

From: Yannick Vignon <yannick.vignon@nxp.com>

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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/ethernet/stmicro/stmmac/stmmac_hwtstamp.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

--- 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 *

static void get_systime(void __iomem *ioaddr, u64 *systime)
{
- u64 ns;
+ u64 ns, 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;
+ /* 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)