Date: Wed, 3 Jul 2024 14:47:57 +0000
From: "D, Lakshmi Sowjanya" <lakshmi.sowjanya.d@...el.com>
To: "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>
CC: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.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>, "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


> -----Original Message-----
> From: D, Lakshmi Sowjanya <lakshmi.sowjanya.d@...el.com>
> Sent: Wednesday, June 12, 2024 9:24 AM
> To: tglx@...utronix.de; giometti@...eenne.com; corbet@....net; linux-
> kernel@...r.kernel.org; linux-doc@...r.kernel.org
> Cc: gregkh@...uxfoundation.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>; D, Lakshmi Sowjanya
> <lakshmi.sowjanya.d@...el.com>
> Subject: [PATCH v10 0/3] Add support for Intel PPS Generator
> 
> 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].
> 
> Please help to review the changes.
> 
> Thanks in advance,
> Sowjanya
> 
> Changes from v2:
>  - Split patch 1 to remove the functions in later stages.
>  - Include required headers in pps_gen_tio.
> 
> Changes from v3:
>  - Corrections in Documentation.
>  - Introducing non-RFC version of the patch series.
> 
> Changes from v4:
>  - Setting id in ice_ptp
>  - Modified conversion logic in convert_base_to_cs.
>  - Included the usage of the APIs in the commit message of 2nd patch.
> 
> Changes from v5:
>  - Change nsecs variable to use_nsecs.
>  - Change order of 1&2 patches and modify the commit message.
>  - Add sysfs abi file entry in MAINTAINERS file.
>  - Add check to find if any event is missed and disable hardware
>    accordingly.
> 
> Changes from v6:
>  - Split patch 1 into 1&2 patches.
>  - Add check for overflow in convert_ns_to_cs().
>  - Refine commit messages.
> 
> Changes from v7:
>  - Split the if condition and return error if current time exceeds
>    expire time.
>  - Update kernel version and month in ABI file.
> 
> Changes from v8:
>  - Add function to enable Timed I/O.
>  - Changed the updating of tio->enabled to a centralized place in
>    disable and enable functions.
> 
> Changes from v9:
>  - use tio->enabled instead of reading ctrl register.
>  - change error code in enable_store to -ENODEV.
> 
> Lakshmi Sowjanya D (3):
>   pps: generators: Add PPS Generator TIO Driver
>   Documentation: driver-api: pps: Add Intel Timed I/O PPS generator
>   ABI: pps: Add ABI documentation for Intel TIO
> 
>  .../ABI/testing/sysfs-platform-pps-tio        |   7 +
>  Documentation/driver-api/pps.rst              |  24 ++
>  MAINTAINERS                                   |   1 +
>  drivers/pps/generators/Kconfig                |  16 ++
>  drivers/pps/generators/Makefile               |   1 +
>  drivers/pps/generators/pps_gen_tio.c          | 264 ++++++++++++++++++
>  6 files changed, 313 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-platform-pps-tio
>  create mode 100644 drivers/pps/generators/pps_gen_tio.c
> 
> --
> 2.35.3

Hi,

A gentle reminder for the review of the pps patchset.

Regards
Sowjanya

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