pftf
Support for external RTC.
Today the time/date is not kept across power state transitions. This is not a bug, because the Pi hardware has no RTC.
There are however Pi Hats with RTCs. It would be interesting to support such a hat (or hats). Of course, it needs to be done in way that doesn't break base Pi support.
I have an i2c RTC module. Before using UEFI Firmware, I can add a udev rule that lets OS see the rtc device After using UEFI Firmware, I found that UEFI Firmware will virtualize an rtc device (but the time is the same every time I boot ), and the /sys/class/i2c-adapter is empty, Raspberry Pi 4 UEFI Firmware Images does not support i2c yet? If so, what do I need to do to get the OS to see i2c devices, such as config.txt?
I have an i2c RTC module. Before using UEFI Firmware, I can add a udev rule that lets OS see the rtc device After using UEFI Firmware, I found that UEFI Firmware will virtualize an rtc device (but the time is the same every time I boot ), and the /sys/class/i2c-adapter is empty, Raspberry Pi 4 UEFI Firmware Images does not support i2c yet? If so, what do I need to do to get the OS to see i2c devices, such as config.txt?
You can't currently use I2C in Linux if you boot using UEFI. There are two reasons for this: 1) The kernel doesn't know how to attach the driver based on the information in the ACPI tables, 2) pin muxing isn't setup correctly.
I have been able to use I2C from UEFI on a modified kernel with a modified firmware (I needed to initialise the pinmux from the firmware). Those patches aren't really in a state where I can share them since I had to hard-code the frequency of the clock driving the I2C block(s). I'm happy to clean them up and post them if I'm able to solve that issue though. See #130 for I2C support.
I hooked up the existing ds1307 driver, to the rpi's I2C1, and spent a whole bunch of time messing with depex/etc to get it to load automatically when enabled. The changes can be found here: https://github.com/jlinton/edk2-platforms/tree/cppc6-various-fixes-vc4aml-mailboxspinlock-xhcipci-clocktweaks-spiv5
The device I've been testing it with: https://www.amazon.com/Makerfire%C2%AE-Raspberry-Module-DS1307-Battery/dp/B00ZOXWHK4
