Yes. rtc0 is registered as shown below:
$ dmesg -T | grep rtc
[Tue Sep 6 12:17:58 2022] iommu: Adding device bc00000.rtcpu to group 23
[Tue Sep 6 12:17:58 2022] vdd-rtc: at 800 mV
[Tue Sep 6 12:17:59 2022] camchar: rtcpu character device driver loaded
[Tue Sep 6 12:17:59 2022] rtc rtc0: alarm rtc device
[Tue Sep 6 12:17:59 2022] max77686-rtc max77620-rtc: rtc core: registered max77620-rtc as rtc0
[Tue Sep 6 12:17:59 2022] tegra186-cam-rtcpu bc00000.rtcpu: deferring, 14800000.isp is not probed
[Tue Sep 6 12:18:03 2022] tegra186-cam-rtcpu bc00000.rtcpu: Trace buffer configured at IOVA=0xbff00000
[Tue Sep 6 12:18:04 2022] tegra-ivc ivc-bc00000.rtcpu: region 0: iova=0xbfee0000-0xbfefffff size=131072
[Tue Sep 6 12:18:04 2022] tegra-ivc ivc-bc00000.rtcpu:echo@0: echo: ver=0 grp=1 RX[16x64]=0x1000-0x1480 TX[16x64]=0x1480-0x1900
[Tue Sep 6 12:18:04 2022] tegra-ivc ivc-bc00000.rtcpu:dbg@1: dbg: ver=0 grp=1 RX[1x384]=0x1900-0x1b00 TX[1x384]=0x1b00-0x1d00
[Tue Sep 6 12:18:04 2022] tegra-ivc ivc-bc00000.rtcpu:dbg@2: dbg: ver=0 grp=1 RX[1x8192]=0x1d00-0x3d80 TX[1x8192]=0x3d80-0x5e00
[Tue Sep 6 12:18:04 2022] tegra-ivc ivc-bc00000.rtcpu:ivccontrol@3: ivccontrol: ver=0 grp=1 RX[64x320]=0x5e00-0xae80 TX[64x320]=0xae80-0xff00
[Tue Sep 6 12:18:04 2022] tegra-capture-ivc ivc-bc00000.rtcpu:ivccontrol@3: no priority specified, using 99 as default
[Tue Sep 6 12:18:04 2022] tegra-ivc ivc-bc00000.rtcpu:ivccapture@4: ivccapture: ver=0 grp=1 RX[512x64]=0xff00-0x17f80 TX[512x64]=0x17f80-0x20000
[Tue Sep 6 12:18:04 2022] tegra-capture-ivc ivc-bc00000.rtcpu:ivccapture@4: no priority specified, using 99 as default
[Tue Sep 6 12:18:04 2022] tegra186-cam-rtcpu bc00000.rtcpu: using cam RTCPU IRQ (71)
[Tue Sep 6 12:18:04 2022] tegra186-cam-rtcpu bc00000.rtcpu: tegra_camrtc_mon_create is successful
[Tue Sep 6 12:18:04 2022] tegra186-cam-rtcpu bc00000.rtcpu: firmware version cpu=rce cmd=5 sha1=8966ca7b0e527ed98649649b043322724401969c
[Tue Sep 6 12:18:04 2022] max77686-rtc max77620-rtc: setting system clock to 2000-01-01 01:03:06 UTC (946688586)
Done but no success.
As I am directly building kernel on the jetson, I found two place where CONFIG_RTC_HCTOSYS_DEVICE was defined.
jetson@ubuntu:~/Linux_for_Tegra/source$ grep -rnw . -e CONFIG_RTC_HCTOSYS_DEVICE
...
./public/kernel/kernel-4.9/arch/arm64/configs/tegra_defconfig:1012:CONFIG_RTC_HCTOSYS_DEVICE="rtc1"
./public/kernel/kernel-4.9/.config:4808:CONFIG_RTC_HCTOSYS_DEVICE="rtc1
...
I modified both of them to rtc0 before buliding the kernel.
$ grep -r CONFIG_RTC_HCTOSYS_DEVICE ~/Linux_for_Tegra/source/public/kernel/kernel-4.9/arch/arm64/configs/tegra_defconfig
CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
$ grep -r CONFIG_RTC_HCTOSYS_DEVICE ~/Linux_for_Tegra/source/public/kernel/kernel-4.9/.config
CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
I kept the device off for 20 minutes and then turned it on to check the time. It was incorrect. Please note that before tuning off the device the time was corrected manually as ntp is disabled.
$ timedatectl
Local time: Tue 2022-09-06 12:18:53 JST
Universal time: Tue 2022-09-06 03:18:53 UTC
RTC time: Sat 2000-01-01 01:03:54
Time zone: Asia/Tokyo (JST, +0900)
System clock synchronized: no
systemd-timesyncd.service active: no
RTC in local TZ: no