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

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Date: Tue, 9 Jan 2024 06:31:32 +0000
From: "D, Lakshmi Sowjanya" <lakshmi.sowjanya.d@...el.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "jstultz@...gle.com"
	<jstultz@...gle.com>, "giometti@...eenne.com" <giometti@...eenne.com>,
	"corbet@....net" <corbet@....net>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>, "Dong,
 Eddie" <eddie.dong@...el.com>, "Hall, Christopher S"
	<christopher.s.hall@...el.com>, "Brandeburg, Jesse"
	<jesse.brandeburg@...el.com>, "davem@...emloft.net" <davem@...emloft.net>,
	"alexandre.torgue@...s.st.com" <alexandre.torgue@...s.st.com>,
	"joabreu@...opsys.com" <joabreu@...opsys.com>, "mcoquelin.stm32@...il.com"
	<mcoquelin.stm32@...il.com>, "perex@...ex.cz" <perex@...ex.cz>,
	"linux-sound@...r.kernel.org" <linux-sound@...r.kernel.org>, "Nguyen, Anthony
 L" <anthony.l.nguyen@...el.com>, "N, Pandith" <pandith.n@...el.com>,
	"Sangannavar, Mallikarjunappa" <mallikarjunappa.sangannavar@...el.com>, "T R,
 Thejesh Reddy" <thejesh.reddy.t.r@...el.com>, Peter Hilber
	<peter.hilber@...nsynergy.com>
Subject: RE: [RFC PATCH v3 00/11] Add support for Intel PPS Generator



> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Sent: Saturday, January 6, 2024 8:50 PM
> To: D, Lakshmi Sowjanya <lakshmi.sowjanya.d@...el.com>
> Cc: tglx@...utronix.de; jstultz@...gle.com; giometti@...eenne.com;
> corbet@....net; linux-kernel@...r.kernel.org; x86@...nel.org;
> netdev@...r.kernel.org; linux-doc@...r.kernel.org; intel-wired-
> lan@...ts.osuosl.org; Dong, Eddie <eddie.dong@...el.com>; Hall, Christopher S
> <christopher.s.hall@...el.com>; Brandeburg, Jesse
> <jesse.brandeburg@...el.com>; davem@...emloft.net;
> alexandre.torgue@...s.st.com; joabreu@...opsys.com;
> mcoquelin.stm32@...il.com; perex@...ex.cz; linux-sound@...r.kernel.org;
> Nguyen, Anthony L <anthony.l.nguyen@...el.com>; N, Pandith
> <pandith.n@...el.com>; Sangannavar, Mallikarjunappa
> <mallikarjunappa.sangannavar@...el.com>; T R, Thejesh Reddy
> <thejesh.reddy.t.r@...el.com>
> 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@...el.com
> wrote:
> > From: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
> >
> > 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@opensynergy.com/T/ which is RFC.

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