| Message ID | 20250219193306.1045-1-quic_philber@quicinc.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Add virtio_rtc module | expand |
On Wed, Feb 19, 2025 at 08:32:55PM +0100, Peter Hilber wrote: > This series implements a driver for a virtio-rtc device conforming to spec > proposal v7 [1]. It includes a PTP clock driver and an RTC class driver > with alarm. > > v5 updates > ========== > > Important changes compared to the previous driver series [3] are: > > - Update to spec proposal v7 [1]. > > - Fix multiple initialization related bugs. > > - Drop the RFC tag, since no major outstanding issues are apparent. > > Overview > ======== > > This patch series adds the virtio_rtc module, and related bugfixes. The > virtio_rtc module implements a driver compatible with the proposed Virtio > RTC device specification [1]. The Virtio RTC (Real Time Clock) device > provides information about current time. The device can provide different > clocks, e.g. for the UTC or TAI time standards, or for physical time > elapsed since some past epoch. The driver can read the clocks with simple > or more accurate methods. Optionally, the driver can set an alarm. > > For the Virtio RTC device, there is currently a proprietary implementation, > which has been used for testing. > > PTP clock interface > =================== > > virtio_rtc exposes clocks as PTP clocks to userspace, similar to ptp_kvm. > If both the Virtio RTC device and this driver have special support for the > current clocksource, time synchronization programs can use > cross-timestamping using ioctl PTP_SYS_OFFSET_PRECISE2 aka > PTP_SYS_OFFSET_PRECISE. Similar to ptp_kvm, system time synchronization > with single-digit ns precision is possible with a quiescent reference clock > (from the Virtio RTC device). This works even when the Virtio device > response is slow compared to ptp_kvm hypercalls. > > The following illustrates a test using PTP_SYS_OFFSET_PRECISE, with > interspersed strace log and chrony [2] refclocks log, on arm64. In the > example, chrony tracks a virtio_rtc PTP clock ("PHCV", /dev/ptp0). The raw > offset between the virtio_rtc clock and CLOCK_REALTIME is 0 to 1 ns. At the > device side, the Virtio RTC device artificially delays both the clock read > request, and the response, by 50 ms. Cross-timestamp interpolation still > works with this delay. chrony also monitors a ptp_kvm clock ("PHCK", > /dev/ptp3) for comparison, which yields a similar offset. > > ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000329> > =============================================================================== > Date (UTC) Time Refid DP L P Raw offset Cooked offset Disp. > =============================================================================== > 2023-06-29 18:49:55.595742 PHCK 0 N 0 1.000000e-09 8.717931e-10 5.500e-08 > 2023-06-29 18:49:55.595742 PHCK - N - - 8.717931e-10 5.500e-08 > ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101545> > 2023-06-29 18:49:56.147766 PHCV 0 N 0 1.000000e-09 8.801870e-10 5.500e-08 > 2023-06-29 18:49:56.147766 PHCV - N - - 8.801870e-10 5.500e-08 > ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000195> > 2023-06-29 18:49:56.202446 PHCK 0 N 0 1.000000e-09 7.364180e-10 5.500e-08 > 2023-06-29 18:49:56.202446 PHCK - N - - 7.364180e-10 5.500e-08 > ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101484> > 2023-06-29 18:49:56.754641 PHCV 0 N 0 0.000000e+00 -2.617368e-10 5.500e-08 > 2023-06-29 18:49:56.754641 PHCV - N - - -2.617368e-10 5.500e-08 > ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000270> > 2023-06-29 18:49:56.809282 PHCK 0 N 0 1.000000e-09 7.779321e-10 5.500e-08 > 2023-06-29 18:49:56.809282 PHCK - N - - 7.779321e-10 5.500e-08 > ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101510> > 2023-06-29 18:49:57.361376 PHCV 0 N 0 0.000000e+00 -2.198794e-10 5.500e-08 > 2023-06-29 18:49:57.361376 PHCV - N - - -2.198794e-10 5.500e-08 > > This patch series only adds special support for the Arm Generic Timer > clocksource. At the driver side, it should be easy to support more > clocksources. > > Fallback PTP clock interface > ---------------------------- > > Without special support for the current clocksource, time synchronization > programs can still use ioctl PTP_SYS_OFFSET_EXTENDED2 aka > PTP_SYS_OFFSET_EXTENDED. In this case, precision will generally be worse > and will depend on the Virtio device response characteristics. > > The following illustrates a test using PTP_SYS_OFFSET_EXTENDED, with > interspersed strace log and chrony refclocks log, on x86-64 (with `ts' > values omitted): > > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > =============================================================================== > Date (UTC) Time Refid DP L P Raw offset Cooked offset Disp. > =============================================================================== > 2023-06-28 14:11:26.697782 PHCV 0 N 0 3.318200e-05 3.450891e-05 4.611e-06 > 2023-06-28 14:11:26.697782 PHCV - N - - 3.450891e-05 4.611e-06 > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > 2023-06-28 14:11:27.208763 PHCV 0 N 0 -3.792800e-05 -4.023965e-05 4.611e-06 > 2023-06-28 14:11:27.208763 PHCV - N - - -4.023965e-05 4.611e-06 > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > 2023-06-28 14:11:27.722818 PHCV 0 N 0 -3.328600e-05 -3.134404e-05 4.611e-06 > 2023-06-28 14:11:27.722818 PHCV - N - - -3.134404e-05 4.611e-06 > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > 2023-06-28 14:11:28.233572 PHCV 0 N 0 -4.966900e-05 -4.584331e-05 4.611e-06 > 2023-06-28 14:11:28.233572 PHCV - N - - -4.584331e-05 4.611e-06 > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > 2023-06-28 14:11:28.742737 PHCV 0 N 0 4.902700e-05 5.361388e-05 4.611e-06 > 2023-06-28 14:11:28.742737 PHCV - N - - 5.361388e-05 4.611e-06 > > PTP clock setup > --------------- > > The following udev rule can be used to get a symlink /dev/ptp_virtio to the > UTC clock: > > SUBSYSTEM=="ptp", ATTR{clock_name}=="Virtio PTP type 0, variant 0", SYMLINK += "ptp_virtio" > > The following chrony configuration directive can then be added in > /etc/chrony/chrony.conf to synchronize to the Virtio UTC clock: > > refclock PHC /dev/ptp_virtio refid PHCV poll -1 dpoll -1 > > RTC interface > ============= > > This patch series adds virtio_rtc as a generic Virtio driver, including > both a PTP clock driver and an RTC class driver. > > Feedback is greatly appreciated. > > [1] https://lore.kernel.org/virtio-comment/20250123101616.664-1-quic_philber@quicinc.com/ > [2] https://chrony.tuxfamily.org/ > [3] https://lore.kernel.org/lkml/20241219201118.2233-1-quic_philber@quicinc.com/ > > Changelog > ========= > > v5: > > - Update to virtio-rtc spec v7, essentially removing definitions. > > - Fix multiple bugs after readying device during probe and restore. > > - Actually initialize Virtio clock id for RTC class device. > > - Add freeze/restore ops already in first patch. > > - Minor changes: > > - Use new APIs devm_device_init_wakeup(), secs_to_jiffies(). > > - Fix style issues. > > - Improve logging types and clarity. > > - Drop unnecessary memory barrier pair. > > - Return error status from device, whenever available. > > v4: > > - Update Virtio interface to spec v6. > > - Distinguish UTC-like clocks by handling of leap seconds (spec v6). > > - Do not create RTC class device for clocks which may step on leap seconds > (Alexandre Belloni). > > - Clear RTC class feature bit instead of defining reduced ops > (Alexandre Belloni). > > - For PTP clock name, always use numeric clock type, and numeric variant. > > - Use macros for 64-bit divisions. > > - Remove unnecessary memory barriers. > > - Cosmetic improvements. > > - Drop upstreamed timekeeping bugfixes from series. > > v3: > > - Update to conform to virtio spec RFC v3 (no significant behavioral > changes). > > - Add RTC class driver with alarm according to virtio spec RFC v3. > > - For cross-timestamp corner case fix, switch back to v1 style closed > interval test (Thomas Gleixner). > > v2: > > - Depend on patch series "treewide: Use clocksource id for > get_device_system_crosststamp()" to avoid requiring a clocksource pointer > with get_device_system_crosststamp(). > > - Assume Arm Generic Timer will use CP15 virtual counter. Drop > arm_arch_timer helper functions (Marc Zyngier). > > - Improve cross-timestamp fixes problem description and implementation > (John Stultz). > > > Peter Hilber (4): > virtio_rtc: Add module and driver core > virtio_rtc: Add PTP clocks > virtio_rtc: Add Arm Generic Timer cross-timestamping > virtio_rtc: Add RTC class driver > > MAINTAINERS | 7 + > drivers/virtio/Kconfig | 64 ++ > drivers/virtio/Makefile | 5 + > drivers/virtio/virtio_rtc_arm.c | 23 + > drivers/virtio/virtio_rtc_class.c | 262 +++++ > drivers/virtio/virtio_rtc_driver.c | 1404 ++++++++++++++++++++++++++ > drivers/virtio/virtio_rtc_internal.h | 122 +++ > drivers/virtio/virtio_rtc_ptp.c | 347 +++++++ > include/uapi/linux/virtio_rtc.h | 237 +++++ Also, should this driver live under ./drivers/rtc/virtio/ ? > 9 files changed, 2471 insertions(+) > create mode 100644 drivers/virtio/virtio_rtc_arm.c > create mode 100644 drivers/virtio/virtio_rtc_class.c > create mode 100644 drivers/virtio/virtio_rtc_driver.c > create mode 100644 drivers/virtio/virtio_rtc_internal.h > create mode 100644 drivers/virtio/virtio_rtc_ptp.c > create mode 100644 include/uapi/linux/virtio_rtc.h > > > base-commit: 8936cec5cb6e27649b86fabf383d7ce4113bba49 > -- > 2.43.0
On Tue, Feb 25, 2025 at 07:18:59AM -0500, Michael S. Tsirkin wrote: > On Wed, Feb 19, 2025 at 08:32:55PM +0100, Peter Hilber wrote: > > This series implements a driver for a virtio-rtc device conforming to spec > > proposal v7 [1]. It includes a PTP clock driver and an RTC class driver > > with alarm. > > > > v5 updates > > ========== > > > > Important changes compared to the previous driver series [3] are: > > > > - Update to spec proposal v7 [1]. > > > > - Fix multiple initialization related bugs. > > > > - Drop the RFC tag, since no major outstanding issues are apparent. > > > > Overview > > ======== > > > > This patch series adds the virtio_rtc module, and related bugfixes. The > > virtio_rtc module implements a driver compatible with the proposed Virtio > > RTC device specification [1]. The Virtio RTC (Real Time Clock) device > > provides information about current time. The device can provide different > > clocks, e.g. for the UTC or TAI time standards, or for physical time > > elapsed since some past epoch. The driver can read the clocks with simple > > or more accurate methods. Optionally, the driver can set an alarm. > > > > For the Virtio RTC device, there is currently a proprietary implementation, > > which has been used for testing. > > > > PTP clock interface > > =================== > > > > virtio_rtc exposes clocks as PTP clocks to userspace, similar to ptp_kvm. > > If both the Virtio RTC device and this driver have special support for the > > current clocksource, time synchronization programs can use > > cross-timestamping using ioctl PTP_SYS_OFFSET_PRECISE2 aka > > PTP_SYS_OFFSET_PRECISE. Similar to ptp_kvm, system time synchronization > > with single-digit ns precision is possible with a quiescent reference clock > > (from the Virtio RTC device). This works even when the Virtio device > > response is slow compared to ptp_kvm hypercalls. > > > > The following illustrates a test using PTP_SYS_OFFSET_PRECISE, with > > interspersed strace log and chrony [2] refclocks log, on arm64. In the > > example, chrony tracks a virtio_rtc PTP clock ("PHCV", /dev/ptp0). The raw > > offset between the virtio_rtc clock and CLOCK_REALTIME is 0 to 1 ns. At the > > device side, the Virtio RTC device artificially delays both the clock read > > request, and the response, by 50 ms. Cross-timestamp interpolation still > > works with this delay. chrony also monitors a ptp_kvm clock ("PHCK", > > /dev/ptp3) for comparison, which yields a similar offset. > > > > ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000329> > > =============================================================================== > > Date (UTC) Time Refid DP L P Raw offset Cooked offset Disp. > > =============================================================================== > > 2023-06-29 18:49:55.595742 PHCK 0 N 0 1.000000e-09 8.717931e-10 5.500e-08 > > 2023-06-29 18:49:55.595742 PHCK - N - - 8.717931e-10 5.500e-08 > > ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101545> > > 2023-06-29 18:49:56.147766 PHCV 0 N 0 1.000000e-09 8.801870e-10 5.500e-08 > > 2023-06-29 18:49:56.147766 PHCV - N - - 8.801870e-10 5.500e-08 > > ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000195> > > 2023-06-29 18:49:56.202446 PHCK 0 N 0 1.000000e-09 7.364180e-10 5.500e-08 > > 2023-06-29 18:49:56.202446 PHCK - N - - 7.364180e-10 5.500e-08 > > ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101484> > > 2023-06-29 18:49:56.754641 PHCV 0 N 0 0.000000e+00 -2.617368e-10 5.500e-08 > > 2023-06-29 18:49:56.754641 PHCV - N - - -2.617368e-10 5.500e-08 > > ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000270> > > 2023-06-29 18:49:56.809282 PHCK 0 N 0 1.000000e-09 7.779321e-10 5.500e-08 > > 2023-06-29 18:49:56.809282 PHCK - N - - 7.779321e-10 5.500e-08 > > ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101510> > > 2023-06-29 18:49:57.361376 PHCV 0 N 0 0.000000e+00 -2.198794e-10 5.500e-08 > > 2023-06-29 18:49:57.361376 PHCV - N - - -2.198794e-10 5.500e-08 > > > > This patch series only adds special support for the Arm Generic Timer > > clocksource. At the driver side, it should be easy to support more > > clocksources. > > > > Fallback PTP clock interface > > ---------------------------- > > > > Without special support for the current clocksource, time synchronization > > programs can still use ioctl PTP_SYS_OFFSET_EXTENDED2 aka > > PTP_SYS_OFFSET_EXTENDED. In this case, precision will generally be worse > > and will depend on the Virtio device response characteristics. > > > > The following illustrates a test using PTP_SYS_OFFSET_EXTENDED, with > > interspersed strace log and chrony refclocks log, on x86-64 (with `ts' > > values omitted): > > > > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > > =============================================================================== > > Date (UTC) Time Refid DP L P Raw offset Cooked offset Disp. > > =============================================================================== > > 2023-06-28 14:11:26.697782 PHCV 0 N 0 3.318200e-05 3.450891e-05 4.611e-06 > > 2023-06-28 14:11:26.697782 PHCV - N - - 3.450891e-05 4.611e-06 > > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > > 2023-06-28 14:11:27.208763 PHCV 0 N 0 -3.792800e-05 -4.023965e-05 4.611e-06 > > 2023-06-28 14:11:27.208763 PHCV - N - - -4.023965e-05 4.611e-06 > > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > > 2023-06-28 14:11:27.722818 PHCV 0 N 0 -3.328600e-05 -3.134404e-05 4.611e-06 > > 2023-06-28 14:11:27.722818 PHCV - N - - -3.134404e-05 4.611e-06 > > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > > 2023-06-28 14:11:28.233572 PHCV 0 N 0 -4.966900e-05 -4.584331e-05 4.611e-06 > > 2023-06-28 14:11:28.233572 PHCV - N - - -4.584331e-05 4.611e-06 > > ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 > > 2023-06-28 14:11:28.742737 PHCV 0 N 0 4.902700e-05 5.361388e-05 4.611e-06 > > 2023-06-28 14:11:28.742737 PHCV - N - - 5.361388e-05 4.611e-06 > > > > PTP clock setup > > --------------- > > > > The following udev rule can be used to get a symlink /dev/ptp_virtio to the > > UTC clock: > > > > SUBSYSTEM=="ptp", ATTR{clock_name}=="Virtio PTP type 0, variant 0", SYMLINK += "ptp_virtio" > > > > The following chrony configuration directive can then be added in > > /etc/chrony/chrony.conf to synchronize to the Virtio UTC clock: > > > > refclock PHC /dev/ptp_virtio refid PHCV poll -1 dpoll -1 > > > > RTC interface > > ============= > > > > This patch series adds virtio_rtc as a generic Virtio driver, including > > both a PTP clock driver and an RTC class driver. > > > > Feedback is greatly appreciated. > > > > [1] https://lore.kernel.org/virtio-comment/20250123101616.664-1-quic_philber@quicinc.com/ > > [2] https://chrony.tuxfamily.org/ > > [3] https://lore.kernel.org/lkml/20241219201118.2233-1-quic_philber@quicinc.com/ > > > > Changelog > > ========= > > > > v5: > > > > - Update to virtio-rtc spec v7, essentially removing definitions. > > > > - Fix multiple bugs after readying device during probe and restore. > > > > - Actually initialize Virtio clock id for RTC class device. > > > > - Add freeze/restore ops already in first patch. > > > > - Minor changes: > > > > - Use new APIs devm_device_init_wakeup(), secs_to_jiffies(). > > > > - Fix style issues. > > > > - Improve logging types and clarity. > > > > - Drop unnecessary memory barrier pair. > > > > - Return error status from device, whenever available. > > > > v4: > > > > - Update Virtio interface to spec v6. > > > > - Distinguish UTC-like clocks by handling of leap seconds (spec v6). > > > > - Do not create RTC class device for clocks which may step on leap seconds > > (Alexandre Belloni). > > > > - Clear RTC class feature bit instead of defining reduced ops > > (Alexandre Belloni). > > > > - For PTP clock name, always use numeric clock type, and numeric variant. > > > > - Use macros for 64-bit divisions. > > > > - Remove unnecessary memory barriers. > > > > - Cosmetic improvements. > > > > - Drop upstreamed timekeeping bugfixes from series. > > > > v3: > > > > - Update to conform to virtio spec RFC v3 (no significant behavioral > > changes). > > > > - Add RTC class driver with alarm according to virtio spec RFC v3. > > > > - For cross-timestamp corner case fix, switch back to v1 style closed > > interval test (Thomas Gleixner). > > > > v2: > > > > - Depend on patch series "treewide: Use clocksource id for > > get_device_system_crosststamp()" to avoid requiring a clocksource pointer > > with get_device_system_crosststamp(). > > > > - Assume Arm Generic Timer will use CP15 virtual counter. Drop > > arm_arch_timer helper functions (Marc Zyngier). > > > > - Improve cross-timestamp fixes problem description and implementation > > (John Stultz). > > > > > > Peter Hilber (4): > > virtio_rtc: Add module and driver core > > virtio_rtc: Add PTP clocks > > virtio_rtc: Add Arm Generic Timer cross-timestamping > > virtio_rtc: Add RTC class driver > > > > MAINTAINERS | 7 + > > drivers/virtio/Kconfig | 64 ++ > > drivers/virtio/Makefile | 5 + > > drivers/virtio/virtio_rtc_arm.c | 23 + > > drivers/virtio/virtio_rtc_class.c | 262 +++++ > > drivers/virtio/virtio_rtc_driver.c | 1404 ++++++++++++++++++++++++++ > > drivers/virtio/virtio_rtc_internal.h | 122 +++ > > drivers/virtio/virtio_rtc_ptp.c | 347 +++++++ > > include/uapi/linux/virtio_rtc.h | 237 +++++ > > > Also, should this driver live under > ./drivers/rtc/virtio/ > > ? It has a PTP clock driver as well, so I think drivers/rtc would not be the best location. I tried to avoid splitting the driver across subsystems. Maybe it could live under drivers/virtio/rtc, if you don't like having 5 new files in the directory? Thanks for the comment, Peter > > > > > 9 files changed, 2471 insertions(+) > > create mode 100644 drivers/virtio/virtio_rtc_arm.c > > create mode 100644 drivers/virtio/virtio_rtc_class.c > > create mode 100644 drivers/virtio/virtio_rtc_driver.c > > create mode 100644 drivers/virtio/virtio_rtc_internal.h > > create mode 100644 drivers/virtio/virtio_rtc_ptp.c > > create mode 100644 include/uapi/linux/virtio_rtc.h > > > > > > base-commit: 8936cec5cb6e27649b86fabf383d7ce4113bba49 > > -- > > 2.43.0 >
This series implements a driver for a virtio-rtc device conforming to spec proposal v7 [1]. It includes a PTP clock driver and an RTC class driver with alarm. v5 updates ========== Important changes compared to the previous driver series [3] are: - Update to spec proposal v7 [1]. - Fix multiple initialization related bugs. - Drop the RFC tag, since no major outstanding issues are apparent. Overview ======== This patch series adds the virtio_rtc module, and related bugfixes. The virtio_rtc module implements a driver compatible with the proposed Virtio RTC device specification [1]. The Virtio RTC (Real Time Clock) device provides information about current time. The device can provide different clocks, e.g. for the UTC or TAI time standards, or for physical time elapsed since some past epoch. The driver can read the clocks with simple or more accurate methods. Optionally, the driver can set an alarm. For the Virtio RTC device, there is currently a proprietary implementation, which has been used for testing. PTP clock interface =================== virtio_rtc exposes clocks as PTP clocks to userspace, similar to ptp_kvm. If both the Virtio RTC device and this driver have special support for the current clocksource, time synchronization programs can use cross-timestamping using ioctl PTP_SYS_OFFSET_PRECISE2 aka PTP_SYS_OFFSET_PRECISE. Similar to ptp_kvm, system time synchronization with single-digit ns precision is possible with a quiescent reference clock (from the Virtio RTC device). This works even when the Virtio device response is slow compared to ptp_kvm hypercalls. The following illustrates a test using PTP_SYS_OFFSET_PRECISE, with interspersed strace log and chrony [2] refclocks log, on arm64. In the example, chrony tracks a virtio_rtc PTP clock ("PHCV", /dev/ptp0). The raw offset between the virtio_rtc clock and CLOCK_REALTIME is 0 to 1 ns. At the device side, the Virtio RTC device artificially delays both the clock read request, and the response, by 50 ms. Cross-timestamp interpolation still works with this delay. chrony also monitors a ptp_kvm clock ("PHCK", /dev/ptp3) for comparison, which yields a similar offset. ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000329> =============================================================================== Date (UTC) Time Refid DP L P Raw offset Cooked offset Disp. =============================================================================== 2023-06-29 18:49:55.595742 PHCK 0 N 0 1.000000e-09 8.717931e-10 5.500e-08 2023-06-29 18:49:55.595742 PHCK - N - - 8.717931e-10 5.500e-08 ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101545> 2023-06-29 18:49:56.147766 PHCV 0 N 0 1.000000e-09 8.801870e-10 5.500e-08 2023-06-29 18:49:56.147766 PHCV - N - - 8.801870e-10 5.500e-08 ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000195> 2023-06-29 18:49:56.202446 PHCK 0 N 0 1.000000e-09 7.364180e-10 5.500e-08 2023-06-29 18:49:56.202446 PHCK - N - - 7.364180e-10 5.500e-08 ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101484> 2023-06-29 18:49:56.754641 PHCV 0 N 0 0.000000e+00 -2.617368e-10 5.500e-08 2023-06-29 18:49:56.754641 PHCV - N - - -2.617368e-10 5.500e-08 ioctl(5</dev/ptp3>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.000270> 2023-06-29 18:49:56.809282 PHCK 0 N 0 1.000000e-09 7.779321e-10 5.500e-08 2023-06-29 18:49:56.809282 PHCK - N - - 7.779321e-10 5.500e-08 ioctl(6</dev/ptp0>, PTP_SYS_OFFSET_PRECISE, 0xffffe86691c8) = 0 <0.101510> 2023-06-29 18:49:57.361376 PHCV 0 N 0 0.000000e+00 -2.198794e-10 5.500e-08 2023-06-29 18:49:57.361376 PHCV - N - - -2.198794e-10 5.500e-08 This patch series only adds special support for the Arm Generic Timer clocksource. At the driver side, it should be easy to support more clocksources. Fallback PTP clock interface ---------------------------- Without special support for the current clocksource, time synchronization programs can still use ioctl PTP_SYS_OFFSET_EXTENDED2 aka PTP_SYS_OFFSET_EXTENDED. In this case, precision will generally be worse and will depend on the Virtio device response characteristics. The following illustrates a test using PTP_SYS_OFFSET_EXTENDED, with interspersed strace log and chrony refclocks log, on x86-64 (with `ts' values omitted): ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 =============================================================================== Date (UTC) Time Refid DP L P Raw offset Cooked offset Disp. =============================================================================== 2023-06-28 14:11:26.697782 PHCV 0 N 0 3.318200e-05 3.450891e-05 4.611e-06 2023-06-28 14:11:26.697782 PHCV - N - - 3.450891e-05 4.611e-06 ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 2023-06-28 14:11:27.208763 PHCV 0 N 0 -3.792800e-05 -4.023965e-05 4.611e-06 2023-06-28 14:11:27.208763 PHCV - N - - -4.023965e-05 4.611e-06 ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 2023-06-28 14:11:27.722818 PHCV 0 N 0 -3.328600e-05 -3.134404e-05 4.611e-06 2023-06-28 14:11:27.722818 PHCV - N - - -3.134404e-05 4.611e-06 ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 2023-06-28 14:11:28.233572 PHCV 0 N 0 -4.966900e-05 -4.584331e-05 4.611e-06 2023-06-28 14:11:28.233572 PHCV - N - - -4.584331e-05 4.611e-06 ioctl(5, PTP_SYS_OFFSET_EXTENDED, {n_samples=10, ts=OMITTED}) = 0 2023-06-28 14:11:28.742737 PHCV 0 N 0 4.902700e-05 5.361388e-05 4.611e-06 2023-06-28 14:11:28.742737 PHCV - N - - 5.361388e-05 4.611e-06 PTP clock setup --------------- The following udev rule can be used to get a symlink /dev/ptp_virtio to the UTC clock: SUBSYSTEM=="ptp", ATTR{clock_name}=="Virtio PTP type 0, variant 0", SYMLINK += "ptp_virtio" The following chrony configuration directive can then be added in /etc/chrony/chrony.conf to synchronize to the Virtio UTC clock: refclock PHC /dev/ptp_virtio refid PHCV poll -1 dpoll -1 RTC interface ============= This patch series adds virtio_rtc as a generic Virtio driver, including both a PTP clock driver and an RTC class driver. Feedback is greatly appreciated. [1] https://lore.kernel.org/virtio-comment/20250123101616.664-1-quic_philber@quicinc.com/ [2] https://chrony.tuxfamily.org/ [3] https://lore.kernel.org/lkml/20241219201118.2233-1-quic_philber@quicinc.com/ Changelog ========= v5: - Update to virtio-rtc spec v7, essentially removing definitions. - Fix multiple bugs after readying device during probe and restore. - Actually initialize Virtio clock id for RTC class device. - Add freeze/restore ops already in first patch. - Minor changes: - Use new APIs devm_device_init_wakeup(), secs_to_jiffies(). - Fix style issues. - Improve logging types and clarity. - Drop unnecessary memory barrier pair. - Return error status from device, whenever available. v4: - Update Virtio interface to spec v6. - Distinguish UTC-like clocks by handling of leap seconds (spec v6). - Do not create RTC class device for clocks which may step on leap seconds (Alexandre Belloni). - Clear RTC class feature bit instead of defining reduced ops (Alexandre Belloni). - For PTP clock name, always use numeric clock type, and numeric variant. - Use macros for 64-bit divisions. - Remove unnecessary memory barriers. - Cosmetic improvements. - Drop upstreamed timekeeping bugfixes from series. v3: - Update to conform to virtio spec RFC v3 (no significant behavioral changes). - Add RTC class driver with alarm according to virtio spec RFC v3. - For cross-timestamp corner case fix, switch back to v1 style closed interval test (Thomas Gleixner). v2: - Depend on patch series "treewide: Use clocksource id for get_device_system_crosststamp()" to avoid requiring a clocksource pointer with get_device_system_crosststamp(). - Assume Arm Generic Timer will use CP15 virtual counter. Drop arm_arch_timer helper functions (Marc Zyngier). - Improve cross-timestamp fixes problem description and implementation (John Stultz). Peter Hilber (4): virtio_rtc: Add module and driver core virtio_rtc: Add PTP clocks virtio_rtc: Add Arm Generic Timer cross-timestamping virtio_rtc: Add RTC class driver MAINTAINERS | 7 + drivers/virtio/Kconfig | 64 ++ drivers/virtio/Makefile | 5 + drivers/virtio/virtio_rtc_arm.c | 23 + drivers/virtio/virtio_rtc_class.c | 262 +++++ drivers/virtio/virtio_rtc_driver.c | 1404 ++++++++++++++++++++++++++ drivers/virtio/virtio_rtc_internal.h | 122 +++ drivers/virtio/virtio_rtc_ptp.c | 347 +++++++ include/uapi/linux/virtio_rtc.h | 237 +++++ 9 files changed, 2471 insertions(+) create mode 100644 drivers/virtio/virtio_rtc_arm.c create mode 100644 drivers/virtio/virtio_rtc_class.c create mode 100644 drivers/virtio/virtio_rtc_driver.c create mode 100644 drivers/virtio/virtio_rtc_internal.h create mode 100644 drivers/virtio/virtio_rtc_ptp.c create mode 100644 include/uapi/linux/virtio_rtc.h base-commit: 8936cec5cb6e27649b86fabf383d7ce4113bba49