linux-kernel - Re: [V2 3/4] Documentation pps.rst: add PPS generators documentation

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Message-ID: <07528a82-13ee-421f-8ad9-e99689d4f03a@infradead.org>
Date: Thu, 31 Oct 2024 10:14:03 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: Rodolfo Giometti <giometti@...eenne.com>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, Greg KH <greg@...ah.com>,
 corbet@....net, Hall Christopher S <christopher.s.hall@...el.com>,
 Mohan Subramanian <subramanian.mohan@...el.com>, tglx@...utronix.de,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Dong Eddie <eddie.dong@...el.com>, N Pandith <pandith.n@...el.com>,
 T R Thejesh Reddy <thejesh.reddy.t.r@...el.com>,
 Zage David <david.zage@...el.com>,
 Chinnadurai Srinivasan <srinivasan.chinnadurai@...el.com>
Subject: Re: [V2 3/4] Documentation pps.rst: add PPS generators documentation



On 10/31/24 9:35 AM, Rodolfo Giometti wrote:
> This patch adds some examples about how to register a new PPS
> generator in the system, and how to manage it.
> 
> Signed-off-by: Rodolfo Giometti <giometti@...eenne.com>
> ---
>  Documentation/driver-api/pps.rst | 40 ++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
> 
> diff --git a/Documentation/driver-api/pps.rst b/Documentation/driver-api/pps.rst
> index 78dded03e5d8..dffa06ed919f 100644
> --- a/Documentation/driver-api/pps.rst
> +++ b/Documentation/driver-api/pps.rst
> @@ -202,6 +202,46 @@ Sometimes one needs to be able not only to catch PPS signals but to produce
>  them also. For example, running a distributed simulation, which requires
>  computers' clock to be synchronized very tightly.
>  
> +To do so the class pps-gen has been added. PPS generators can be
> +registered in the kernel by defining a struct pps_gen_source_info as
> +follows::
> +
> +    static struct pps_gen_source_info pps_gen_dummy_info = {
> +            .name                   = "dummy",
> +            .use_system_clock       = true,
> +            .get_time               = pps_gen_dummy_get_time,
> +            .enable                 = pps_gen_dummy_enable,
> +    };
> +
> +Where the use_system_clock states if the generator uses the system
> +clock to generate its pulses, or from a peripheral device

                                 or they are from a peripheral device

> +clock. Method get_time() is used to query the time stored into the
> +generator clock, while the method enable() is used to enable or
> +disable the PPS pulse generation.
> +
> +Then calling the function pps_gen_register_source() in your
> +initialization routine as follows creates a new generator in the
> +system::
> +
> +    pps_gen = pps_gen_register_source(&pps_gen_dummy_info);
> +
> +Generators SYSFS support
> +------------------------
> +
> +If the SYSFS filesystem is enabled in the kernel it provides a new class::
> +
> +    $ ls /sys/class/pps-gen/
> +    pps-gen0/  pps-gen1/  pps-gen2/
> +
> +Every directory is the ID of a PPS generator defined in the system and
> +inside you find several files::
> +
> +    $ ls -F /sys/class/pps-gen/pps-gen0/
> +    dev  enable  name  power/  subsystem@  system  time  uevent
> +
> +To enable the PPS signal generation you can use the command below::
> +
> +    $ echo 1 > /sys/class/pps-gen/pps-gen0/enable
>  
>  Parallel port generator
>  ------------------------

-- 
~Randy