Messages in this thread | | | Date | Thu, 3 Feb 2022 16:44:24 +0000 | From | "Russell King (Oracle)" <> | Subject | Re: [PATCH net] net: stmmac: ensure PTP time register reads are consistent |
| |
On Thu, Feb 03, 2022 at 05:38:10PM +0100, Yannick Vignon wrote: > On 2/3/2022 5:28 PM, Russell King (Oracle) wrote: > > On Thu, Feb 03, 2022 at 05:00:25PM +0100, Yannick Vignon wrote: > > > From: Yannick Vignon <yannick.vignon@nxp.com> > > > > > > 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. > > > > Have you checked whether the hardware protects against this (i.o.w. the > > hardware latches the PTP_STSR value when PTP_STNSR is read, or vice > > versa? Several PTP devices I've looked at do this to allow consistent > > reading. > > > > It doesn't. I was able to observe inconsistent values doing reads in either > order, and we had already observed the issue with that same IP on another > device (Cortex-M based, not running Linux). It's not easy to reproduce, the > time window is small, but it's there.
Okay, thanks.
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
| |