On 2026-10-17T18:46:22, Hung-Chun Tseng <[email protected]> wrote: > virtio: rtc: Add virtio RTC driver > > Add a driver for the virtio RTC device (virtio device ID 17), which > QEMU provides as virtio-rtc-pci and virtio-rtc-device since v11.1.0. > > The device exposes its clocks through a request virtqueue. As the > virtqueue must not be used before the virtio uclass sets DRIVER_OK, > which happens after probe(), the first read looks for the clock: it > asks for the number of clocks with VIRTIO_RTC_REQ_CFG and queries the > type of each with VIRTIO_RTC_REQ_CLOCK_CAP. Reading the time sends a > VIRTIO_RTC_REQ_READ for the chosen clock and converts the nanoseconds > since the epoch with rtc_to_tm(). Each request gives up with > -ETIMEDOUT if the device does not answer within a second, as virtio_9p > does. The clocks are read-only, so there is no set operation, and the > optional alarm feature is not negotiated. > > Like Linux, the driver prefers a VIRTIO_RTC_CLOCK_UTC_SMEARED clock. > Linux registers an RTC class device only for such a clock and skips > VIRTIO_RTC_CLOCK_UTC and VIRTIO_RTC_CLOCK_UTC_MAYBE_SMEARED, which may > step on leap seconds. QEMU, however, exposes a single clock of type > VIRTIO_RTC_CLOCK_UTC, so following Linux strictly would leave U-Boot > without an RTC there. If no clock smears leap seconds, the driver > therefore falls back to the first UTC or maybe-smeared UTC clock. A > leap second step matters little to U-Boot, which only reads the time. > > Like Linux, the driver stops looking for a clock as soon as a request > fails. After a timeout the request is still on the virtqueue, so its > late response could be taken for that of a later request. > > VIRTIO_RTC defaults to y when VIRTIO and DM_RTC are enabled, like > VIRTIO_RNG does for DM_RNG. > > If none of the clocks is UTC, the driver remembers it and fails later > reads with -ENODEV at once, as the set of clocks never changes. > > Tested with QEMU v11.1.2 on qemu-riscv64 over both PCI and MMIO. > Sandbox tests, which emulate the device, follow later in this series. > > Signed-off-by: Hung-Chun Tseng <[email protected]> > > drivers/virtio/Kconfig | 11 ++ > drivers/virtio/Makefile | 1 + > drivers/virtio/virtio-uclass.c | 1 + > drivers/virtio/virtio_rtc.c | 249 > +++++++++++++++++++++++++++++++++++++++++ > include/virtio.h | 4 +- > 5 files changed, 265 insertions(+), 1 deletion(-)
Reviewed-by: Simon Glass <[email protected]>
