[PATCH v2 2/2] rtc: provide an emulated RTC

[Grant Likely]

On Sun, Oct 25, 2020 at 7:13 AM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
>
> On a board without hardware clock this software real time clock can be
> used. The build time is used to initialize the RTC. So you will have
> to adjust the time either manually using the 'date' command  or use
> the 'sntp' to update the RTC with the time from a network time server.
> See CONFIG_CMD_SNTP and CONFIG_BOOTP_NTPSERVER. The RTC time is
> advanced according to CPU ticks.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>

Looks good to me, and tested on RockPro64 w/ UEFI SCT.

Tested-by: Grant Likely <grant.likely at arm.com>

g.

> ---
> v2:
>         more elaborate Kconfig message
>         adjust device name properties
>         use build time as initial time
> ---
>  MAINTAINERS            |  1 +
>  drivers/rtc/Kconfig    | 11 ++++++
>  drivers/rtc/Makefile   |  1 +
>  drivers/rtc/emul_rtc.c | 80 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 93 insertions(+)
>  create mode 100644 drivers/rtc/emul_rtc.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index fc4fad46ee..a98e0c5b76 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -678,6 +678,7 @@ S:  Maintained
>  T:     git https://gitlab.denx.de/u-boot/custodians/u-boot-efi.git
>  F:     doc/api/efi.rst
>  F:     doc/uefi/*
> +F:     drivers/rtc/emul_rtc.c
>  F:     include/capitalization.h
>  F:     include/charset.h
>  F:     include/cp1250.h
> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> index 63662001c2..d06d272e14 100644
> --- a/drivers/rtc/Kconfig
> +++ b/drivers/rtc/Kconfig
> @@ -63,6 +63,17 @@ config RTC_DS3232
>           Support for Dallas Semiconductor (now Maxim) DS3232 compatible
>           Real Time Clock devices.
>
> +config RTC_EMULATION
> +       bool "Enable emulated RTC"
> +       depends on DM_RTC
> +       help
> +         On a board without hardware clock this software real time clock can be
> +         used. The build time is used to initialize the RTC. So you will have
> +         to adjust the time either manually using the 'date' command  or use
> +         the 'sntp' to update the RTC with the time from a network time server.
> +         See CONFIG_CMD_SNTP and CONFIG_BOOTP_NTPSERVER. The RTC time is
> +         advanced according to CPU ticks.
> +
>  config RTC_ISL1208
>         bool "Enable ISL1208 driver"
>         depends on DM_RTC
> diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
> index 12eb449583..ef66dc4bf0 100644
> --- a/drivers/rtc/Makefile
> +++ b/drivers/rtc/Makefile
> @@ -22,6 +22,7 @@ obj-$(CONFIG_RTC_DS164x) += ds164x.o
>  obj-$(CONFIG_RTC_DS174x) += ds174x.o
>  obj-$(CONFIG_RTC_DS3231) += ds3231.o
>  obj-$(CONFIG_RTC_DS3232) += ds3232.o
> +obj-$(CONFIG_RTC_EMULATION) += emul_rtc.o
>  obj-$(CONFIG_RTC_FTRTC010) += ftrtc010.o
>  obj-$(CONFIG_SANDBOX) += i2c_rtc_emul.o
>  obj-$(CONFIG_RTC_IMXDI) += imxdi.o
> diff --git a/drivers/rtc/emul_rtc.c b/drivers/rtc/emul_rtc.c
> new file mode 100644
> index 0000000000..c98c24bbb3
> --- /dev/null
> +++ b/drivers/rtc/emul_rtc.c
> @@ -0,0 +1,80 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright 2020, Heinrich Schuchardt <xypron.glpk at gmx.de>
> + *
> + * This driver emulates a real time clock based on timer ticks.
> + */
> +
> +#include <common.h>
> +#include <div64.h>
> +#include <dm.h>
> +#include <generated/timestamp_autogenerated.h>
> +#include <rtc.h>
> +
> +/**
> + * struct emul_rtc - private data for emulated RTC driver
> + */
> +struct emul_rtc {
> +       /**
> +        * @offset_us: microseconds from 1970-01-01 to timer_get_us() base
> +        */
> +       u64 offset_us;
> +       /**
> +        * @isdst: daylight saving time
> +        */
> +       int isdst;
> +};
> +
> +static int emul_rtc_get(struct udevice *dev, struct rtc_time *time)
> +{
> +       struct emul_rtc *priv = dev_get_priv(dev);
> +       u64 now;
> +
> +       if (!priv->offset_us) {
> +               /* Use the build date as initial time */
> +               priv->offset_us = U_BOOT_EPOCH * 1000000ULL - timer_get_us();
> +               priv->isdst = -1;
> +       }
> +
> +       now = timer_get_us() + priv->offset_us;
> +       do_div(now, 1000000);
> +       rtc_to_tm(now, time);
> +       time->tm_isdst = priv->isdst;
> +
> +       return 0;
> +}
> +
> +static int emul_rtc_set(struct udevice *dev, const struct rtc_time *time)
> +{
> +       struct emul_rtc *priv = dev_get_priv(dev);
> +
> +       if (time->tm_year < 1970)
> +               return -EINVAL;
> +
> +       priv->offset_us = rtc_mktime(time) * 1000000ULL - timer_get_us();
> +
> +       if (time->tm_isdst > 0)
> +               priv->isdst = 1;
> +       else if (time->tm_isdst < 0)
> +               priv->isdst = -1;
> +       else
> +               priv->isdst = 0;
> +
> +       return 0;
> +}
> +
> +static const struct rtc_ops emul_rtc_ops = {
> +       .get = emul_rtc_get,
> +       .set = emul_rtc_set,
> +};
> +
> +U_BOOT_DRIVER(rtc_emul) = {
> +       .name   = "rtc_emul",
> +       .id     = UCLASS_RTC,
> +       .ops    = &emul_rtc_ops,
> +       .priv_auto_alloc_size = sizeof(struct emul_rtc),
> +};
> +
> +U_BOOT_DEVICE(rtc_emul) = {
> +       .name   = "rtc_emul",
> +};
> --
> 2.28.0
>