RE: [PATCH v10 0/4] virtio-rtc: Add device specification

> From: Matias Ezequiel Vara Larsen <[email protected]>
> Sent: 22 September 2025 07:24 PM
> 
> @parav I think this has been voted on. Should it be merged in 1.4?
>
On it.
Was on travel for whole of last week.
Starting work today.
 
> Matias
> 
> On Thu, Jul 10, 2025 at 11:16 AM Peter Hilber <[email protected]>
> wrote:
> >
> > On Thu, Jul 10, 2025 at 11:06:45AM +0200, Peter Hilber wrote:
> > > This iteration of the spec fixes merge conflicts with the recently
> > > merged virtio-media device and adds two missing entries in the
> > > Conformance section.
> > >
> > > Summary
> > > -------
> > >
> > > The RTC (Real Time Clock) device provides information about current
> > > time. The device can provide different clocks, for the UTC or TAI
> > > time standards, or for physical time elapsed since some past epoch.
> > > For UTC clocks, the device can also indicate how leap seconds are
> > > handled. The driver can read the clocks with simple or more accurate
> methods.
> > > Optionally, the driver can set an alarm.
> > >
> > > The driver-side timekeeping can synchronize precisely to a local
> > > clock exposed by the RTC device. If supported by the device, the
> > > driver can obtain a cross-timestamp from the local clock and the
> > > system hardware counter, in a way similar to the Linux kernel ptp_kvm
> driver [1].
> > >
> > > The alarm allows the driver side to be woken up from a sleep state
> > > at a specific time.
> >
> > Could you please open a voting ballot for these changes?
> >
> > Fixes: https://github.com/oasis-tcs/virtio-spec/issues/221
> >
> > Apparently no ballot has been opened for v9. I am now requesting one
> > for the v10 (with changes as mentioned at the top).
> >
> > Best regards,
> >
> > Peter
> >
> > >
> > > Changelog
> > > ---------
> > >
> > > v10:
> > >
> > > - Add RTC clauses to the "Conformance Targets" section.
> > >
> > > - Fix merge conflicts with recently merged virtio-media device.
> > >
> > > v9:
> > >
> > > - Add motivation to cover letter (Michael S. Tsirkin).
> > >
> > > - Allow more implementation-specific behavior when alarm actions
> become
> > >   obsolete (Matias Ezequiel Vara Larsen).
> > >
> > > - Define how device should not change across resets (Michael S. Tsirkin).
> > >
> > > - Document that device converts hardware counter value, accounting for
> > >   device/driver differences in offset/multiplier (Michael S. Tsirkin).
> > >
> > > - Restrict implementation-specific id ranges to experimental
> > >   implementations (Michael S. Tsirkin).
> > >
> > > - Mandate that only flags allowed by negotiated features may be accessed
> > >   (Michael S. Tsirkin).
> > >
> > > - State that an error-free device sets status OK for all requests from a
> > >   well-behaved driver (Michael S. Tsirkin).
> > >
> > > - Change name to "Real Time Clock" in device type list (Michael S.
> > >   Tsirkin).
> > >
> > > - Remove unneeded requirement about what to put into device-readable
> > >   buffers (Matias Ezequiel Vara Larsen).
> > >
> > > - Reword multiple sentences and requirements (Matias Ezequiel Vara
> Larsen,
> > >   Michael S. Tsirkin).
> > >
> > > - Move fixes which were mistakenly placed in patch 2 in v8 (Cornelia
> Huck).
> > >
> > > - Remove statement implying that device MUST NOT check that reserved
> fields
> > >   are zero.
> > >
> > > v8:
> > >
> > > - Explicitly describe alarm enabled status, where relevant (Matias Ezequiel
> > >   Vara Larsen).
> > >
> > > - Reword multiple sentences and requirements (Matias Ezequiel Vara
> Larsen).
> > >
> > > - Drop unnecessary or redundant requirements (Matias Ezequiel Vara
> Larsen).
> > >
> > > - Change word order from "field X" to "the X field" (Matias Ezequiel Vara
> > >   Larsen).
> > >
> > > - Change word order from "flag X" to "the X flag" or "X".
> > >
> > > - Move requirements to serve alarm expiration events before
> requirements
> > >   about stopping to serve (Matias Ezequiel Vara Larsen).
> > >
> > > v7:
> > >
> > > - Remove leap second and performance indications from struct
> > >   virtio_rtc_resp_read_cross. Remove backing definitions.
> > >
> > > - Move wording change which was mistakenly placed in last patch to first
> > >   patch.
> > >
> > > v6:
> > >
> > > - Make leap second status information optional if the clock smears (or
> > >   might smear) leap seconds.
> > >
> > > - Do not use union for leap second indication.
> > >
> > > - Improve wording.
> > >
> > > - Refer to the new POSIX.1-2024 for UTC epoch definition.
> > >
> > > v5:
> > >
> > > - Change structure and wording to support adding shared memory like
> > >   vmclock [2].
> > >
> > > - Add dedicated clock types for UTC leap second smearing (David
> > >   Woodhouse).
> > >
> > > - Extend leap second indications.
> > >
> > > - Replace VIRTIO_RTC_SUBTYPE_ by VIRTIO_RTC_SMEAR_.
> > >
> > > - For Arm Generic Timer, only support Virtual Count Register (David
> > >   Woodhouse).
> > >
> > > - Rename MONO clock to MONOTONIC clock.
> > >
> > > - Harmonize bit widths with vmclock [2].
> > >
> > > - Change formatting.
> > >
> > > v4:
> > >
> > > - Distinguish UTC clocks with and without leap smearing (David
> > >   Woodhouse).
> > >
> > > - Add UTC leap second and TAI offset indication (David Woodhouse).
> > >
> > > - Add clock performance information (David Woodhouse).
> > >
> > > - Drop distinction of Arm Generic Timer virtual and physical counter.
> > >
> > > - Change requirements so that driver can reset alarm to clean slate, and
> > >   document how driver can achieve this (Cornelia Hell, Jason Wang).
> > >
> > > - Device should assume that driver reads clock from first vCPU (David
> > >   Woodhouse).
> > >
> > > - Driver should read clock to confirm that alarm has expired.
> > >
> > > - Require driver to set unused flags to zero.
> > >
> > > - Require device to support all expressible alarm times.
> > >
> > > - Formatting and wording improvements.
> > >
> > > v3:
> > >
> > > - Address comments from Parav Pandit.
> > >
> > > - Add an optional alarm feature.
> > >
> > > - Various other changes.
> > >
> > > v2:
> > >
> > > - Address comments from Cornelia Huck.
> > >
> > > [1]
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/c
> > > ommit/?id=a0e136d436ded817c0aade72efdefa56a00b4e5e
> > > [2]
> > > https://lore.kernel.org/lkml/20240708092924.1473461-1-
> dwmw2@infradea
> > > d.org/
> > >
> > >
> > > Peter Hilber (4):
> > >   virtio-rtc: Add initial device specification
> > >   virtio-rtc: Add initial normative statements
> > >   virtio-rtc: Add alarm feature
> > >   virtio-rtc: Add normative statements for alarm feature
> > >
> > >  conformance.tex                         |   12 +-
> > >  content.tex                             |    3 +-
> > >  device-types/rtc/description.tex        | 1117 +++++++++++++++++++++++
> > >  device-types/rtc/device-conformance.tex |   13 +
> > >  device-types/rtc/driver-conformance.tex |   11 +
> > >  introduction.tex                        |    6 +
> > >  6 files changed, 1157 insertions(+), 5 deletions(-)  create mode
> > > 100644 device-types/rtc/description.tex  create mode 100644
> > > device-types/rtc/device-conformance.tex
> > >  create mode 100644 device-types/rtc/driver-conformance.tex
> > >
> > >
> > > base-commit: c5e5810cb6cb48b673bd3247eb48490d29b1e0fb
> > > --
> > > 2.43.0
> > >
> >