netdev - Re: [chrony-dev] Support for Multiple PPS Inputs on single PHC

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Message-ID: <5bfd4360-2bee-80c1-2b46-84b97f5a039c@bluematt.me>
Date:   Thu, 23 Feb 2023 12:56:34 -0800
From:   Matt Corallo <ntp-lists@...tcorallo.com>
To:     Richard Cochran <richardcochran@...il.com>,
        Miroslav Lichvar <mlichvar@...hat.com>
Cc:     chrony-dev@...ony.tuxfamily.org,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [chrony-dev] Support for Multiple PPS Inputs on single PHC

On 2/20/23 7:24 AM, Richard Cochran wrote:
> On Mon, Feb 20, 2023 at 11:08:23AM +0100, Miroslav Lichvar wrote:
>> Does it need to be that way? It seems strange for the kernel to
>> support enabling PPS on multiple channels at the same time, but not
>> allow multiple applications to receive all samples from their channel.
> 
> It does not need to be that way, but nobody ever wanted multiple
> readers before.
> 
> Implementing this would make the kernel side much more complex, as the
> code would need per-reader tracking of the buffered time stamps, or
> per-reader fifo buffers, etc.

There's two separate questions here - multiple readers receiving the same data, and multiple readers 
receiving data exclusively about one channel.

I'd imagine the second is (much?) easier to implement, whereas the first is a bunch of complexity.

At least personally I'm okay with the second, rather than the first, and that fixes the issue for 
chrony, though it doesn't allow one to, say, get raw samples in one program while having another 
handle them.

Matt