RE: [RFC PATCH v3 00/11] Add support for Intel PPS Generator

[D, Lakshmi Sowjanya]

> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Sent: Saturday, January 6, 2024 8:50 PM
> To: D, Lakshmi Sowjanya <lakshmi.sowjanya.d@xxxxxxxxx>
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> <mallikarjunappa.sangannavar@xxxxxxxxx>; T R, Thejesh Reddy
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> Subject: Re: [RFC PATCH v3 00/11] Add support for Intel PPS Generator
> 
> On Wed, Jan 03, 2024 at 05:25:51PM +0530, lakshmi.sowjanya.d@xxxxxxxxx
> wrote:
> > From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@xxxxxxxxx>
> >
> > The goal of the PPS(Pulse Per Second) hardware/software is to generate
> > a signal from the system on a wire so that some third-party hardware
> > can observe that signal and judge how close the system's time is to
> > another system or piece of hardware.
> >
> > Existing methods (like parallel ports) require software to flip a bit
> > at just the right time to create a PPS signal. Many things can prevent
> > software from doing this precisely. This (Timed I/O) method is better
> > because software only "arms" the hardware in advance and then depends
> > on the hardware to "fire" and flip the signal at just the right time.
> >
> > To generate a PPS signal with this new hardware, the kernel wakes up
> > twice a second, once for 1->0 edge and other for the 0->1 edge. It
> > does this shortly (~10ms) before the actual change in the signal needs
> > to be made. It computes the TSC value at which edge will happen,
> > convert to a value hardware understands and program this value to Timed I/O
> hardware.
> > The actual edge transition happens without any further action from the
> > kernel.
> >
> > The result here is a signal coming out of the system that is roughly
> > 1,000 times more accurate than the old methods. If the system is
> > heavily loaded, the difference in accuracy is larger in old methods.
> > Facebook and Google are the customers that use this feature.
> >
> > Application Interface:
> > The API to use Timed I/O is very simple. It is enabled and disabled by
> > writing a '1' or '0' value to the sysfs enable attribute associated
> > with the Timed I/O PPS device. Each Timed I/O pin is represented by a
> > PPS device. When enabled, a pulse-per-second(PPS) synchronized with
> > the system clock is continuously produced on the Timed I/O pin,
> > otherwise it is pulled low.
> >
> > The Timed I/O signal on the motherboard is enabled in the BIOS setup.
> 
> At some point you should announce v1 of the series. RFC is usually being
> neglected by many (busy) maintainers.

This patch series is dependent on https://lore.kernel.org/netdev/20231215220612.173603-2-peter.hilber@xxxxxxxxxxxxxxx/T/ which is RFC.

Regards,
Sowjanya
> 
> --
> With Best Regards,
> Andy Shevchenko
>