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

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Message-ID: <2024092624-stapling-clock-5fe0@gregkh>
Date: Thu, 26 Sep 2024 11:34:38 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Rodolfo Giometti <giometti@...eenne.com>
Cc: "Hall, Christopher S" <christopher.s.hall@...el.com>,
	"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>
Subject: Re: [PATCH v12 2/3] Documentation: driver-api: pps: Add Intel Timed
 I/O PPS generator

On Thu, Sep 26, 2024 at 10:46:54AM +0200, Rodolfo Giometti wrote:
> 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.

This seems sane to me, thanks for writing it up!

greg k-h