linux-kernel - RE: [PATCH v10 0/3] Add support for Intel PPS Generator

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Message-ID: <PH7PR11MB5862AE3F6A9E446A24170064F7872@PH7PR11MB5862.namprd11.prod.outlook.com>
Date: Wed, 14 Aug 2024 04:36:04 +0000
From: "Mohan, Subramanian" <subramanian.mohan@...el.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: "tglx@...utronix.de" <tglx@...utronix.de>, "giometti@...eenne.com"
	<giometti@...eenne.com>, "corbet@....net" <corbet@....net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>,
	"Dong, Eddie" <eddie.dong@...el.com>, "Hall, Christopher S"
	<christopher.s.hall@...el.com>, "N, Pandith" <pandith.n@...el.com>, "T R,
 Thejesh Reddy" <thejesh.reddy.t.r@...el.com>
Subject: RE: [PATCH v10 0/3] Add support for Intel PPS Generator

Hi Greg,

> -----Original Message-----
> From: Greg KH <gregkh@...uxfoundation.org>
> Sent: Tuesday, August 13, 2024 1:46 PM
> To: lakshmi.sowjanya.d@...el.com
> Cc: tglx@...utronix.de; giometti@...eenne.com; corbet@....net; linux-
> kernel@...r.kernel.org; linux-doc@...r.kernel.org;
> andriy.shevchenko@...ux.intel.com; Dong, Eddie <eddie.dong@...el.com>;
> Hall, Christopher S <christopher.s.hall@...el.com>; N, Pandith
> <pandith.n@...el.com>; Mohan, Subramanian
> <subramanian.mohan@...el.com>; T R, Thejesh Reddy
> <thejesh.reddy.t.r@...el.com>
> Subject: Re: [PATCH v10 0/3] Add support for Intel PPS Generator
> 
> On Wed, Jun 12, 2024 at 09:23:56AM +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.
> >
> > 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.
> > Intel Advanced Menu -> PCH IO Configuration -> Timed I/O <Enable>
> >
> > References:
> > https://en.wikipedia.org/wiki/Pulse-per-second_signal
> > https://drive.google.com/file/d/1vkBRRDuELmY8I3FlfOZaEBp-
> DxLW6t_V/view
> > https://youtu.be/JLUTT-lrDqw
> >
> > Patch 1 adds the pps(pulse per second) generator tio driver to the pps
> > subsystem.
> > Patch 2 documentation and usage of the pps tio generator module.
> > Patch 3 includes documentation for sysfs interface.
> >
> > These patches are based on the timers/core branch:
> > [1]
> > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/?h=timers/
> > core These changes are dependent on patches that are merged in [1].
> 
> This series now breaks the build due to api changes in 6.11-rc1.  Please fix up
> and resend.

Ok, will fix up the API changes  and resend the patch series.

> thanks,
> 
> greg k-h

Thanks,
Subbu