Piscenois

Your post is the only one accross the Internet to explain how to activate PWM with RockPi4 and it works ! It deserves to be pinned, tagged. Subliminal message for moderators

I've created the repository on github with all required files, including 2 scripts I'm using to control and query PWM FAN speed.
 
https://github.com/PetrozPL/rockpi4_pwm_overlay
 
Hope You'll find it usefull.
 
EDIT : Also, to control fan speed based on HDD temperature you can use smartctl tool to read HDD temperature from SMART. Example output for my NVMe : 
sudo smartctl -a /dev/nvme0 | grep Temperature Temperature: 76 Celsius Warning Comp. Temperature Time: 0 Critical Comp. Temperature Time: 0 Temperature Sensor 2: 83 Celsius  
If you would like to get system temperature instead hdd You can use another script to check thermal_zone0 temperature: 
#!/bin/bash _temp=`cat /sys/class/thermal/thermal_zone0/temp` _temp1=${_temp::-3} _temp2=${_temp::(-3)} echo ${_temp::-3}.${_temp:(-3)} C  
Best regards,
PetrozPL 
 

With Armbian v20.11 one can write mainline u-boot image to board's SPI and enjoy booting nvme drives without any mmc devices.
Prerequisities: ROCK Pi 4(A/B/C) v1.4 or 1.3 with SPI soldered in (v1.3 comes without SPI flash from the factory).
 
If you already have Radxa's u-boot written to SPI you need to short pins 23 and 25 for Armbian to boot Boot fresh image of Armbian v20.11.x for ROCK Pi 4(A/B/C) Add the following lines to /boot/armbianEnv.txt overlays=spi-jedec-nor param_spinor_spi_bus=1 Reboot If you shorted 23-25 pins in 1.) then: disconnect them after the ROCK Pi 4 fully boot's  enable spi-nor by executing (as root):
echo spi1.0 > /sys/bus/spi/drivers/spi-nor/bind verify that the SPI mtd interface is enabled by running
ls /dev/mtdblock0 if the last command does not list any file then something went wrong between 3.) and 5.) Run nand-sata-install choose option: "Boot from SPI - system on SATA, USB or NVMe" choose NVMe partition, eg. /dev/nvme0n1p1 accept erasing of the choosen partition with "Yes" choose fs type (tested with ext4) wait a few minutes for rootfs transfer to chosen partition choose writing SPI bootloader with "Yes" confirm that you want to flash it with "Yes" wait ~60 seconds for writing choose Exit Reboot Enjoy Armbian booting with SPI / NVMe  
Why bother with mainline u-boot?
It is known to boot some NVMe drives that legacy u-boot from Radxa has issues with, eg. SAMSUNG 970 EVO Plus and SAMSUNG PM981.
This does not mean that all NVMe drives are supported, YMMV.
 
Which NVMe drives are known to be working?
Corsair MP510 240GB/480GB/960GB
Gigabyte SSD M.2 2280 PCIe x2 Model:GP-GSM2NE8128GNTD
HP SSD EX900 M.2 NVMe 120GB. Model: 2YY42AA#ABB
Intel SSD 660p Model:SSDPEKNW512GB
Kingston A1000 SSD 240GB (PHISON PS5008-E8-10)
Kingston A2000 M.2 2280 PCIe NVMe
PNY 250GB XLR8 CS3030 M.2 NVMe SSD PCIe Gen3 x4
Sabrent Rocket 256GB NVMe PCIe M.2 2280
Samsung 970 EVO Plus SSD 250GB M.2 2280, PCIe 3.0 x4, NVMe, 3500/2300 MB/s
Samsung PM981 256GB
XPG SX6000 Lite 128GB (ASX6000LNP-128GT-C)
 
Why not using Radxa's u-boot SPI image?
Ambian's u-boot configuration is incompatible with Radxa's SPI image
 
Why Armbian is using u-boot that is incompatible with Radxa's?
It uses mainline u-boot with Open Source TPL/SPL/proper and BL31 from Rockchip packaged into u-boot and we may switch to using open source ATF instead of the BL31 in the future.
 
Can I boot Radxa's images with Armbian's u-boot written to SPI?
Yes. Armbian's SPI u-boot is compatible with Radxa's images available here: https://github.com/radxa/rock-pi-images-released/releases
It may not be compatible with some older images (released before July 2020) because of the device tree filename change.

ok, I've managed to sort this out on my own. I've decompiled the rockchip-rockpi4.dtb and find out that pwm is disabled by default. So I've wrote new overlay for pwm, just to enable it : 
 
/dts-v1/; / { compatible = "rockchip,rk3399"; fragment@0 { target-path = "/aliases"; __overlay__ { pwm0 = "/pwm@ff420000"; pwm1 = "/pwm@ff420010"; }; }; fragment@1 { target-path = "/pwm@ff420000"; __overlay__ { status = "okay"; }; }; fragment@2 { target-path = "/pwm@ff420010"; __overlay__ { status = "okay"; }; }; }; next, compiled it with dtc : 
dtc -O dtb -o rockchip-pwm-gpio.dtbo -b 0 -@ rockchip-pwm-gpio.dts and moved dtbo to /boot/dtc/rockchip/overlays, and activated it in overlays in /boot/armbianEnv.txt.
 
Now PWM works like a charm. I'm just leaving this thread and my resolution as reference, for anyone with the same problem.
 

Thank you PetrozPL !
I tried pwm, pwm0, pwm1 but no pwm-gpio...
 
Regards.