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

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Message-ID: <2024082456-kitchen-astride-7892@gregkh>
Date: Sat, 24 Aug 2024 10:21:40 +0800
From: Greg KH <gregkh@...uxfoundation.org>
To: subramanian.mohan@...el.com
Cc: tglx@...utronix.de, giometti@...eenne.com, corbet@....net,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	andriy.shevchenko@...ux.intel.com, eddie.dong@...el.com,
	christopher.s.hall@...el.com, pandith.n@...el.com,
	thejesh.reddy.t.r@...el.com, david.zage@...el.com,
	srinivasan.chinnadurai@...el.com
Subject: Re: [PATCH v12 2/3] Documentation: driver-api: pps: Add Intel Timed
 I/O PPS generator

On Fri, Aug 23, 2024 at 12:31:07PM +0530, subramanian.mohan@...el.com wrote:
> From: Subramanian Mohan <subramanian.mohan@...el.com>
> 
> Add Intel Timed I/O PPS usage instructions.
> 
> Co-developed-by: Pandith N <pandith.n@...el.com>
> Signed-off-by: Pandith N <pandith.n@...el.com>
> Signed-off-by: Lakshmi Sowjanya D <lakshmi.sowjanya.d@...el.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Acked-by: Rodolfo Giometti <giometti@...eenne.com>
> Signed-off-by: Subramanian Mohan <subramanian.mohan@...el.com>
> ---
>  Documentation/driver-api/pps.rst | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/Documentation/driver-api/pps.rst b/Documentation/driver-api/pps.rst
> index 78dded03e5d8..75f7b094f963 100644
> --- a/Documentation/driver-api/pps.rst
> +++ b/Documentation/driver-api/pps.rst
> @@ -246,3 +246,27 @@ delay between assert and clear edge as small as possible to reduce system
>  latencies. But if it is too small slave won't be able to capture clear edge
>  transition. The default of 30us should be good enough in most situations.
>  The delay can be selected using 'delay' pps_gen_parport module parameter.
> +
> +
> +Intel Timed I/O PPS signal generator
> +------------------------------------
> +
> +Intel Timed I/O is a high precision device, present on 2019 and newer Intel
> +CPUs, that can generate PPS signals.
> +
> +Timed I/O and system time are both driven by same hardware clock. The signal
> +is generated with a precision of ~20 nanoseconds. The generated PPS signal
> +is used to synchronize an external device with system clock. For example,
> +it can be used to share your clock with a device that receives PPS signal,
> +generated by Timed I/O device. There are dedicated Timed I/O pins to deliver
> +the PPS signal to an external device.
> +
> +Usage of Intel Timed I/O as PPS generator:
> +
> +Start generating PPS signal::
> +
> +        $echo 1 > /sys/devices/platform/INTCxxxx\:00/enable
> +
> +Stop generating PPS signal::
> +
> +        $echo 0 > /sys/devices/platform/INTCxxxx\:00/enable

As I mentioned on the sysfs documentation, why isn't this just a generic
pps class attribute instead?  Why did you make it
only-this-one-special-driver type of thing?

thanks,

greg k-h