[PATCH v6 0/6] virtio: Add a virtio RTC driver

[Hung-Chun Tseng <alan.tseng.cs@gmail.com>]

QEMU v11.1.0 added a virtio RTC device (virtio-rtc-pci and
virtio-rtc-device), but U-Boot has no driver for it. This series adds
one, so that "date" and anything else using dm_rtc_get() work on any
virtio-capable QEMU target.

Patch 1 adds the driver, patch 2 updates the virtio documentation and
patch 3 adds a MAINTAINERS entry. Patch 4 lets sandbox tests answer
virtqueue requests as the device would, which patch 5 uses to test the
driver. Patch 6 documents how to reach the virtio RTC.

Changes in v6:
- Add patch 6, the documentation follow-up Simon suggested on v5, which
  I first sent on its own. Following Simon's review of it, the virtio
  RTC now has its own section, which also takes the QEMU version note
  from patch 2, and x86 is described like ARM and RISC-V: with DM_RTC
  enabled, the MC146818 CMOS RTC gets sequence 0. The Status section
  already lists the RTC since patch 2.
- Rebase onto main. Patches 1-5 are otherwise unchanged.

Tested with qemu-riscv64_smode_defconfig and RTC_GOLDFISH disabled, on
QEMU v11.1.2, which reports a UTC clock, and on QEMU master, which
reports a smeared UTC clock:

- With -device virtio-rtc-pci and with -device virtio-rtc-device,
  "date" reads the host time and advances between reads.
- Setting the time fails, as the clocks are read-only.
- With no virtio RTC device, "date" fails cleanly with err=-19.

With qemu-x86_64_defconfig plus DM_RTC on QEMU v11.1.2, "dm uclass rtc"
shows the CMOS RTC at sequence 0 and the virtio RTC at 1; with
RTC_MC146818 disabled, the virtio RTC is sequence 0 and "date" reads it.

On sandbox, "ut dm virtio_rtc*" passes.

Hung-Chun Tseng (6):
  virtio: rtc: Add virtio RTC driver
  doc: virtio: List the supported device types
  MAINTAINERS: Add entry for virtio RTC
  virtio: sandbox: Let tests emulate the device side of a virtqueue
  test: dm: Add tests for the virtio RTC driver
  doc: virtio: Explain how to reach the virtio RTC

 MAINTAINERS                         |   6 +
 arch/sandbox/dts/test.dts           |   5 +
 arch/sandbox/include/asm/test.h     |  25 +++
 doc/develop/driver-model/virtio.rst |  26 ++-
 drivers/virtio/Kconfig              |  11 +
 drivers/virtio/Makefile             |   1 +
 drivers/virtio/virtio-uclass.c      |   1 +
 drivers/virtio/virtio_rtc.c         | 244 ++++++++++++++++++++++
 drivers/virtio/virtio_sandbox.c     |  15 ++
 include/virtio.h                    |   4 +-
 test/dm/Makefile                    |   1 +
 test/dm/virtio_rtc.c                | 306 ++++++++++++++++++++++++++++
 12 files changed, 640 insertions(+), 5 deletions(-)
 create mode 100644 drivers/virtio/virtio_rtc.c
 create mode 100644 test/dm/virtio_rtc.c

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2.43.0