linux-kernel - Re: [PATCH net-next v7] ptp: Add support for the AMZNC10C 'vmclock' device

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Message-ID: <5077F160-52F0-4E76-B2B9-F0EA9DA76FB4@infradead.org>
Date: Mon, 28 Oct 2024 17:17:14 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Jakub Kicinski <kuba@...nel.org>
CC: Richard Cochran <richardcochran@...il.com>,
 Peter Hilber <peter.hilber@...nsynergy.com>, linux-kernel@...r.kernel.org,
 virtualization@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-rtc@...r.kernel.org, "Ridoux, Julien" <ridouxj@...zon.com>,
 virtio-dev@...ts.linux.dev, "Luu, Ryan" <rluu@...zon.com>,
 "Chashper, David" <chashper@...zon.com>,
 "Mohamed Abuelfotoh, Hazem" <abuehaze@...zon.com>,
 Paolo Abeni <pabeni@...hat.com>,
 "Christopher S . Hall" <christopher.s.hall@...el.com>,
 Jason Wang <jasowang@...hat.com>, John Stultz <jstultz@...gle.com>,
 "Michael S . Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
 Stephen Boyd <sboyd@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Marc Zyngier <maz@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Alessandro Zummo <a.zummo@...ertech.it>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 qemu-devel <qemu-devel@...gnu.org>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net-next v7] ptp: Add support for the AMZNC10C 'vmclock' device

On 28 October 2024 17:12:56 CET, Jakub Kicinski <kuba@...nel.org> wrote:
>On Sat, 19 Oct 2024 18:49:24 +0100 David Woodhouse wrote:
>> > Yes please and thank you! We gotta straighten it out before 
>> > the merge window.  
>> 
>> Hm, as I (finally) come to do that, I realise that many of the others
>> defined in drivers/ptp/Kconfig are also 'default y'. Which is only
>> really 'default PTP_1588_CLOCK' in practice since they all depend on
>> that.
>
>AFAICT nothing defaulted to enabled since 2017, so I'd chalk it up
>to us getting better at catching mistakes over time.
>
>> Most importantly, PTP_1588_CLOCK_KVM is 'default y'. And that one is
>> fundamentally broken (at least in the presence of live migration if
>> guests care about their clock suddenly being wrong) which is why it's
>> being superseded by the new VMCLOCK thing. We absolutely don't want to
>> leave the _KVM one enabled by default and not its _VMCLOCK replacement.
>
>You can default to .._CLOCK_KVM, and provide the explanation in
>the commit message and Kconfig help.

That works for me. But now it's my vacation time so it'll be at least Thursday before I can do that. I'll offer a preemptive Acked-by: David Woodhouse <dwmw@...zon.co.uk> to anyone who beats me to it :)