can not correctly add spi rtc m41t93 chip to raspberry pi 4 64bit.

[gitgonewithwind]

Hi all,
I want to add a spi rtc chip m41t93 to pi 4 64-bit(yocto ,Linux raspberrypi4-64 4.19.66) , I change the kernel config to add CONFIG_RTC_DRV_M41T93=y to make sure the kernel driver is on.
I make sure my rtc hardware board works well, I added it to Maaxboard before, it worked well ,see here: https://community.nxp.com/t5/i-MX-Processors/how-to-make-spi-interface-rtc-function-work-for-imx8mq-maaxboard/m-p/1168938
so similarly, I need to change dtb in pi 4 to make it work, but after I added the blow patch(which is almost same as that I added in maaxboard,see the attached file :0002-rtc-m41t93-patch.txt,the display on webpage is not correct), it does not work in pi 4.
any help?
Thank you very much.

how can I do it?

the debug info:
date --set="20201016 20:56:30"
Fri Oct 16 20:56:30 UTC 2020
root@raspberrypi4-64:# hwclock --systohc --utc --rtc=/dev/rtc0
root@raspberrypi4-64:# dmesg | grep rtc
[ 3.451357] rtc-m41t93 spi0.0: OF bit is set, write time to restart.
[ 3.458578] rtc-m41t93 spi0.0: rtc core: registered rtc-m41t93 as rtc0

dmesg | grep spi
[ 3.472773] rtc-m41t93 spi0.0: rtc core: registered rtc-m41t93 as rtc0
root@raspberrypi4-64:# dmesg | grep rtc
[ 3.472773] rtc-m41t93 spi0.0: rtc core: registered rtc-m41t93 as rtc0
root@raspberrypi4-64:# dmesg | grep spi
[ 3.472773] rtc-m41t93 spi0.0: rtc core: registered rtc-m41t93 as rtc0
root@raspberrypi4-64:~# uname -a
Linux raspberrypi4-64 4.19.66 #1 SMP PREEMPT Tue Sep 21 14:41:35 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux

my patch, I remove spidev0 spidev1, now it is the following:
&spi0 {
pinctrl-names = "default";
pinctrl-0 = <&spi0_pins &spi0_cs_pins>;
cs-gpios = <&gpio 8 1>, <&gpio 7 1>;
status = "okay";
rtc@0 {
compatible = "rtc-m41t93";
reg = <0>;
#address-cells = <1>;
#size-cells = <0>;
spi-max-frequency = <5000000>;
};

};

---

my patch end.

I find someone used the following in raspbian image(not yocto image), but I do not know how to use it and add it where, I list the patch here too:

/dts-v1/;

/plugin/;

/ {

compatible = "brcm,bcm2835";

fragment@0 {

    target = <&spi0>;

    __overlay__ {

        spidev@0 {

            status = "disabled";

        };

        spidev@1 {

            status = "disabled";

        };

        rtc-m41t93@0 {

            compatible = "rtc-m41t93";

            reg = <0>;

            #address-cells = <1>;

            #size-cells = <0>;

            spi-max-frequency = <5000000>;

        };

    };

};

};

0002-rtc-m41t93-patch.txt

[gitgonewithwind]

hi all,
I added a little bit more that my upper post ad following : compatible = "spidev,rtc-m41t93"; (at my first post ,there is no spidev), please see my new attched file: 002-rtc-m41t93.patch-spidev.txt,I remove the orignal &spi0)

now after patched is the following,
I run commanad "hwclock --systohc --utc" and use the scope to capture the wave as the attached files. It seems the cs, clock, miso, mosi are OK,but after power off/on , the date/time is still wrong

any help?
0002-rtc-m41t93.patch-spidev.txt
clock-cls

clock-mosi

mosi-cs

mosi-clock

miso-cs

msio-clock

my patch, I remove spidev0 spidev1, now it is the following:

&spi0 {
pinctrl-names = "default";
pinctrl-0 = <&spi0_pins &spi0_cs_pins>;
cs-gpios = <&gpio 8 1>, <&gpio 7 1>;
status = "okay";
rtc@0 {
compatible = "spidev,rtc-m41t93";
reg = <0>;
#address-cells = <1>;
#size-cells = <0>;
spi-max-frequency = <5000000>;
};

};

[gitgonewithwind]

it strange, why I use hwclock -r to read the rtc chip , the time is correct,
but when I use date to read the time, it always show my compiling kernel time?
what's the problem?
it seems the rtc hardware works??? I use scope to check the wave, I can find the data write and read(not check bit by bit as my pictures posted upper).
see debug info:

root@raspberrypi4-64:# hwclock -r
2021-09-22 11:06:21.860585+00:00
root@raspberrypi4-64:# date
Wed Sep 22 14:32:05 UTC 2021

[gitgonewithwind]

Hi all, I check again, I think my rtc chip is working, set rtc command:"hwclock --systohc --utc". and read rtc command "hwclock -r" work well, but normally, when I use command: "date" to show it, it always shows my kernel compiling time, so the error is in kernel config or in linux system config somewhere?
any help?

[gitgonewithwind]

hi all,
it seems I solve the issue, I add a command line "/sbin/hwclock --hctosys " in my start up scripts, it can read rtc time to linux system time. but I did not do it when I add the rtc chip in maaxboard. it seems the linux system get the rtc time from rtc chip automatically in kernel or somewhere?
any help?
Do I have to add the coomand "/sbin/hwclock --hctosys " in startup script?
thanks

[gitgonewithwind]

HI all,
I find the issue:
need to add config in kernel

CONFIG_RTC_HCTOSYS=y
CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
I am testing...

[gitgonewithwind]

hi all,
it's wired.
I have added
CONFIG_RTC_HCTOSYS=y
CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
in kernel config
and in kernel settings it shows:[*] Set system time from RTC on startup and resume
and my rtc-m41t93 driver is built-in not a module.

but after startup, the date time is still my compilation time.
I have to add "/sbin/hwclock --hctosys " in startup script.
after add "/sbin/hwclock --hctosys ", the date shows correctly.
any help?

[kraj]

if you are using sysvinit then you might want to add rtc to MACHINE_FEATURES

[gitgonewithwind]

if you are using sysvinit then you might want to add rtc to MACHINE_FEATURES

@kraj
let try to add MACHINE_FEATURES_append = " rtc " in local.conf (right??)

I searched online "RTC and System clock not in sync" ,find someone mentioned to use "/sbin/hwclock --hctosys" in init.d .
but before I use maaxboard,did not do anything.( I changed pi 4 kernel config same as maaxboard )

[kraj]

if you are using sysvinit then you might want to add rtc to MACHINE_FEATURES

@kraj
let try to add MACHINE_FEATURES_append = " rtc " in local.conf (right??)

yes

I searched online "RTC and System clock not in sync" ,find someone mentioned to use "/sbin/hwclock --hctosys" in init.d .
but before I use maaxboard,did not do anything.( I changed pi 4 kernel config same as maaxboard )

you need to include the hwclock init scripts and thats what above option will do

[gitgonewithwind]

if you are using sysvinit then you might want to add rtc to MACHINE_FEATURES

@kraj
let try to add MACHINE_FEATURES_append = " rtc " in local.conf (right??)

yes

I searched online "RTC and System clock not in sync" ,find someone mentioned to use "/sbin/hwclock --hctosys" in init.d .
but before I use maaxboard,did not do anything.( I changed pi 4 kernel config same as maaxboard )

you need to include the hwclock init scripts and thats what above option will do

got it. let me do and test. thanks

[gitgonewithwind]

@kraj
sorry, after adding MACHINE_FEATURES_append = " rtc " , the time always is my compilation time.
after I added(or not added) the "/sbin/hwclock --hctosys" in my startup script , the time always are compilation time. can not work well completely.
hwclock -r to read the compilation time. before it can read my setting time. now not!
let me try more tomorrow.

Thu Sep 23 18:20:55 UTC 2021
root@raspberrypi4-64:# hwclock -r
2021-09-23 18:21:03.014401+00:00
root@raspberrypi4-64:# hwclock -r
2021-09-23 18:21:11.621242+00:00
root@raspberrypi4-64:# hwclock -r
2021-09-23 18:21:25.460674+00:00
root@raspberrypi4-64:# hwclock -r
2021-09-23 18:21:27.364927+00:00
root@raspberrypi4-64:# hwclock -r
2021-09-23 18:21:30.488386+00:00
root@raspberrypi4-64:# hwclock -r
2021-09-23 18:21:33.428443+00:00

[gitgonewithwind]

@kraj and all
after reading /etc/init.d/hwclock.sh , I add IMAGE_INSTALL_append = "tzdata" in local.conf and ln -s /usr/share/zoneinfo/America/Toronto /etc/localtime
I make it works well.

Thank you very much.
please close this issue.

[kraj]

thanks closing