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

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Message-ID: <2024081330-retouch-platter-f21d@gregkh>
Date: Tue, 13 Aug 2024 10:15:49 +0200
From: Greg KH <gregkh@...uxfoundation.org>
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, eddie.dong@...el.com,
	christopher.s.hall@...el.com, pandith.n@...el.com,
	subramanian.mohan@...el.com, 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.

thanks,

greg k-h