linux-kernel - Re: [PATCH v12 2/3] Documentation: driver-api: pps: Add Intel Timed I/O PPS generator

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Message-ID: <e88f2d6f-033a-41b5-afdb-8a3f6bcf3d06@enneenne.com>
Date: Thu, 26 Sep 2024 10:46:54 +0200
From: Rodolfo Giometti <giometti@...eenne.com>
To: "Hall, Christopher S" <christopher.s.hall@...el.com>
Cc: "Mohan, Subramanian" <subramanian.mohan@...el.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>, "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>, "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>,
 Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v12 2/3] Documentation: driver-api: pps: Add Intel Timed
 I/O PPS generator

On 25/09/24 23:55, Hall, Christopher S wrote:
> Hi Rodolfo,

Hello.

>> From: Greg KH <gregkh@...uxfoundation.org>
>> Sent: Tuesday, September 03, 2024 3:25 AM
>> To: Rodolfo Giometti <giometti@...eenne.com>
> 
>> Subject: Re: [PATCH v12 2/3] Documentation: driver-api: pps: Add Intel Timed
>> I/O PPS generator
>>
> 
>>> If you are willing to stop the inclusion due this fact maybe its time to add
>>> such PPS generators interface... on the other hand, if you agree for
>>> inclusion we can do this job as soon as the code has been included, in order
>>> to fix this anomalous status.
>>
>> Please make a generic pps subsystem for this, it would make it simpler
>> for everyone.
> 
> What is required to move this? We can certainly test the code and do some
> of this work, but I would look to you to define the interface.

The problem is that a pps-generator has no related device, then no sysfs entries.

I think the right-thing(TM) to do is adding a new class named "pps-generator", 
so we will get the directory /sys/class/pps-generator with several devices as 
pps-generator0, pps-generator1, etc. For each device we should add at least 
these sysfs entries:

- system       : This file return "1" if the generator takes the timing from
                  the system clock, while it returns "0" if not (i.e. from a
                  peripheral device clock).

- time         : This file contains the current time stored into the generator
                  clock as two integers representing the current time seconds and
                  nanoseconds.

- enable       : This write-only file enables or disables generation of the
                  PPS signal.

- period       : This file defines the period for the generator signal. When
                  read, by default, it returns "1 0" which represent the period
                  second and nanoseconds (i.e. a PPS signal). When written, it
                  sets the period accordingly or ENOTSUPP if not supported.

- start_time   : This file defines the starting time for the the generator
                  signal. When read, by default, it returns "0 0" which means
                  "now". When written, it sets the starting time accordingly or
                  ENOTSUPP if not supported.

Please, let me know what do you think about this proposal. I'm going to provide 
a draft in the next weeks since I'm stuck on another project right now. :(

Ciao,

Rodolfo

-- 
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