linux-kernel - Re: [RFC PATCH v2] ptp: Add vDSO-style vmclock support

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Message-ID: <02E9F187-A38C-4D14-A287-AFD7503B6B0F@infradead.org>
Date: Tue, 02 Jul 2024 19:40:04 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: 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>
CC: "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,
 Richard Cochran <richardcochran@...il.com>, 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>
Subject: Re: [RFC PATCH v2] ptp: Add vDSO-style vmclock support

On 2 July 2024 19:12:00 BST, Peter Hilber <peter.hilber@...nsynergy.com> wrote:
>On 02.07.24 18:39, David Woodhouse wrote:
>> To clarify then, the main types are
>> 
>>  VIRTIO_RTC_CLOCK_UTC == 0
>>  VIRTIO_RTC_CLOCK_TAI == 1
>>  VIRTIO_RTC_CLOCK_MONOTONIC == 2
>>  VIRTIO_RTC_CLOCK_SMEARED_UTC == 3
>> 
>> And the subtypes are *only* for the case of
>> VIRTIO_RTC_CLOCK_SMEARED_UTC. They include
>> 
>>  VIRTIO_RTC_SUBTYPE_STRICT
>>  VIRTIO_RTC_SUBTYPE_UNDEFINED /* or whatever you want to call it */
>>  VIRTIO_RTC_SUBTYPE_SMEAR_NOON_LINEAR 
>>  VIRTIO_RTC_SUBTYPE_UTC_SLS /* if it's worth doing this one */
>> 
>> Is that what we just agreed on?
>> 
>> 
>
>This is a misunderstanding. My idea was that the main types are
>
>>  VIRTIO_RTC_CLOCK_UTC == 0
>>  VIRTIO_RTC_CLOCK_TAI == 1
>>  VIRTIO_RTC_CLOCK_MONOTONIC == 2
>>  VIRTIO_RTC_CLOCK_SMEARED_UTC == 3
>
>VIRTIO_RTC_CLOCK_MAYBE_SMEARED_UTC == 4
>
>The subtypes would be (1st for clocks other than
>VIRTIO_RTC_CLOCK_SMEARED_UTC, 2nd to last for
>VIRTIO_RTC_CLOCK_SMEARED_UTC):
>
>#define VIRTIO_RTC_SUBTYPE_STRICT 0
>#define VIRTIO_RTC_SUBTYPE_SMEAR_NOON_LINEAR 1
>#define VIRTIO_RTC_SUBTYPE_SMEAR_UTC_SLS 2
>

Thanks. I really do think that from the guest point of view there's really no distinction between "maybe smeared" and "undefined smearing", and have a preference for using the latter form, which is the key difference there?

Again though, not a hill for me to die on.