On Sat, Oct 31, 2026 at 11:02:07PM +0800, Hung-Chun Tseng wrote: > The date command only uses RTC sequence 0. On the ARM and RISC-V virt > machines that is the PL031 or Goldfish RTC, so date never reads the > virtio RTC unless that driver is disabled. rtc dev does not help, as > rtc read reads raw registers, which the virtio RTC does not have. > > Say this in the virtio documentation, and that x86 needs DM_RTC. > > Suggested-by: Simon Glass <[email protected]> > Signed-off-by: Hung-Chun Tseng <[email protected]> > --- > This is the follow-up Simon suggested on v5. It applies on top of the > v5 series.
Why not send this as v6? Regards, Kuan-Wei > > In my reply to the v5 cover letter I said the doc would point to > "rtc dev" and "rtc read". That was wrong: "rtc dev 1" selects the > virtio RTC, but "rtc read" then fails with -ENOSYS, as the driver > has no register access. > > doc/develop/driver-model/virtio.rst | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/doc/develop/driver-model/virtio.rst > b/doc/develop/driver-model/virtio.rst > index 30df0e944..94d3dabbd 100644 > --- a/doc/develop/driver-model/virtio.rst > +++ b/doc/develop/driver-model/virtio.rst > @@ -81,6 +81,14 @@ on QEMU ARM and x86, and v2.12.0+ on QEMU RISC-V. > The VirtIO RTC device (``-device virtio-rtc-pci`` or > ``-device virtio-rtc-device``) requires QEMU v11.1.0+. > > +The ``date`` command only uses RTC sequence 0. The ARM and RISC-V ``virt`` > +machines also have a PL031 or Goldfish RTC, which gets sequence 0, so > +``date`` reads the VirtIO RTC there only if ``CONFIG_RTC_PL031`` or > +``CONFIG_RTC_GOLDFISH`` is disabled. ``rtc list`` shows the sequence numbers. > +``rtc dev`` does not help, as ``rtc read`` reads raw registers, which the > +VirtIO RTC does not have. On x86, ``CONFIG_DM_RTC`` must be enabled for the > +driver to be built. > + > Testing > ------- > The following QEMU command line is used to get U-Boot up and running with > -- > 2.43.0 >
