linux-kernel - Re: [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO Driver with PHC interface changes to support additional H/W Features

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Message-ID: <20200203040838.GA5851@localhost>
Date:   Sun, 2 Feb 2020 20:08:38 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     christopher.s.hall@...el.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, hpa@...or.com, mingo@...hat.com,
        x86@...nel.org, jacob.e.keller@...el.com, davem@...emloft.net,
        sean.v.kelley@...el.com
Subject: Re: [Intel PMC TGPIO Driver 0/5] Add support for Intel PMC Time GPIO
 Driver with PHC interface changes to support additional H/W Features

On Wed, Dec 11, 2019 at 01:48:47PM -0800, christopher.s.hall@...el.com wrote:
> The ART frequency is not adjustable. In order, to implement output
> adjustments an additional edge-timestamp API is added, as well, as
> a periodic output frequency adjustment API. Togther, these implement
> equivalent functionality to the existing SYS_OFFSET_* and frequency
> adjustment APIs.

I don't see a reason for a custom, new API just for this device.

The TGPIO input clock, the ART, is a free running counter, but you
want to support frequency adjustments.  Use a timecounter cyclecounter
pair.

Let the user dial a periodic output signal in the normal way.

Let the user change the frequency in the normal way, and during this
call, adjust the counter values accordingly.

Thanks,
Richard