Re: PPS functionality for Intel Timed I/O

From: Rodolfo Giometti <giometti@enneenne.com>
To: "N, Pandith" <pandith.n@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Sangannavar,
	Mallikarjunappa"  <mallikarjunappa.sangannavar@intel.com>,
	"D, Lakshmi Sowjanya" <lakshmi.sowjanya.d@intel.com>,
	"T R, Thejesh Reddy" <thejesh.reddy.t.r@intel.com>,
	"Hall, Christopher S" <christopher.s.hall@intel.com>
Subject: Re: PPS functionality for Intel Timed I/O
Date: Mon, 6 Feb 2023 11:46:35 +0100	[thread overview]
Message-ID: <f2788a74-19f8-8992-5b92-427c7b2a27ab@enneenne.com> (raw)
In-Reply-To: <BYAPR11MB32408E2D9758BD01EC65FB49E1DA9@BYAPR11MB3240.namprd11.prod.outlook.com>

On 06/02/23 11:16, N, Pandith wrote:
> Hi Rodolfo,

Hi

>> -----Original Message-----
>> From: Rodolfo Giometti <giometti@enneenne.com>
>> Sent: Monday, January 30, 2023 7:57 PM
>> To: N, Pandith <pandith.n@intel.com>
>> Cc: linux-kernel@vger.kernel.org; Sangannavar, Mallikarjunappa
>> <mallikarjunappa.sangannavar@intel.com>; D, Lakshmi Sowjanya
>> <lakshmi.sowjanya.d@intel.com>; T R, Thejesh Reddy
>> <thejesh.reddy.t.r@intel.com>; Hall, Christopher S
>> <christopher.s.hall@intel.com>
>> Subject: Re: PPS functionality for Intel Timed I/O

>> Within kernel sources PPS clients and PPS generators are placed into different
>> directories, so I suppose is better to deploy two different pieces of code.
>>
> We are planning to add a new PPS generator driver in drivers/pps/generators
> i) Can this driver use pps_register_source to register Intel Timed I/O device for pulse generation ?

Nope. This function is for pps clients only. PPS generators should generate 
their pulses according to system clock so they don't needed any registrations at 
all under PPS layer.

> ii) To start/stop pulse, we are planning to add additional sysfs attribute from our main driver.
> Something like : /sys/class/ppsX/enable_pin
> This is needed for users to start/stop pulse generation.

If you are still talking about PPS generators they have no entries under 
/sys/class/ppsX/ (just clients have). So you can add an entry under your driver 
to do so.

>> However pay attention to the fact that a PPS generator should be referred to
>> system's main clock and not to peripherals' clock.
>>
> We can sync with the system time for pulse generation.

Mmm... I'm not sure this is correct since PPS generators should generate their 
pulses according to system clock and not according to their internal clocks even 
if they are synced with the system clock.

Ciao,

Rodolfo

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