Re: [PATCH net v3] net: ti: icssg-prueth: Fix 1 PPS sync

[Malladi, Meghana]

On 11/5/2024 8:20 AM, Jakub Kicinski wrote:
> On Mon, 4 Nov 2024 16:55:46 +0530 Malladi, Meghana wrote:
> > On 11/1/2024 7:29 AM, Jakub Kicinski wrote:
> > > On Mon, 28 Oct 2024 16:40:52 +0530 Meghana Malladi wrote:
> > > > The first PPS latch time needs to be calculated by the driver
> > > > (in rounded off seconds) and configured as the start time
> > > > offset for the cycle. After synchronizing two PTP clocks
> > > > running as master/slave, missing this would cause master
> > > > and slave to start immediately with some milliseconds
> > > > drift which causes the PPS signal to never synchronize with
> > > > the PTP master.
> > >
> > > You're reading a 64b value in chunks, is it not possible that it'd wrap
> > > in between reads? This can be usually detected by reading high twice and
> > > making sure it didn't change.
> > >
> > > Please fix or explain in the commit message why this is not a problem..
> > Yes I agree that there might be a wrap if the read isn't atomic. As
> > suggested by Andrew I am currently not using custom read where I can
> > implement the logic you suggested
>
> Right but I think Andrew was commenting on a patch which contained pure
> re-implementation of read low / hi with no extra bells or whistles.
>
> > (reading high twice and making sure if
> > didn't change). Can you share me some references where this logic is
> > implemented in the kernel, so I can directly use that instead of writing
> > custom functions.
>
> I think you need to write a custom one. Example:
> https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/tree/drivers/net/ethernet/meta/fbnic/fbnic_time.c#n40
Ok thank you. I will add custom function for this and update the patch.