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

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Message-ID: <ZZlvqvYQQuse_P4E@smile.fi.intel.com>
Date: Sat, 6 Jan 2024 17:20:10 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: 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, eddie.dong@...el.com,
	christopher.s.hall@...el.com, 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, anthony.l.nguyen@...el.com,
	pandith.n@...el.com, mallikarjunappa.sangannavar@...el.com,
	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.

-- 
With Best Regards,
Andy Shevchenko