On 22/05/2023 23:14:54+0200, Marek Behún wrote: > > You probably need to look at rtc-meson-vrtc.c, rtc-fsl-ftm-alarm.c and > > rtc-brcmstb-waketimer.c which implement something similar. > > > > Honestly, I would go for an in-between proposal where you would store > > the requested alarm time (or more likely countdown) on > > set_alarm/alarm_irq_enable so you would get .read_alarm working. > > > > However, my main concern is that this is yet another custom protocol. We > > can't possibly have a driver for everyone implementing a timer in their > > FPGA/CPLD/cortexM. > > > > How will you communicate with the MCU, can't you use an already existing > > driver? > > The MCU exposes a command interface over I2C. There already are > existing commands, which needs to stay for backwards compatibility. > > It is theoretically possible to simulate an existing RTC device on > another I2C address, but I would need to study them, because the boards > are shipped with three different MCUs (STM32, GD32, NXP's MKL81) and > they sometimes have a little different I2C slave behavior. > > But I will need to create a platform/mfd driver anyway for the system > off handler and GPIO controller. If I am going to create a new driver > anyway, why not add the RTC functionality as well? No, this is not how MFD is working, you will be writing a separate RTC driver or reusing an existing one. Have a look at the recent isl1208 series: https://lore.kernel.org/linux-rtc/OS0PR01MB5922DAC377266672ADA9FC28864DA@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/T/#mab0a75187abf7d8aada2c3517ebfdf7241f4bc7a This patch adds supports for the isl1208 on board of a PMIC, as you can see, this is a very small change versus a full blown RTC driver. -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
