Strit has made available linux-rpi4-mainline 5.4.1-1 in the repo for testing if one so desires.
[ray@manjaro ~]$ pacman -Ss linux-rpi4-mainline core/linux-rpi4-mainline 5.4.1-1 [installed] The Linux Kernel and modules - Raspberry Pi 4 64-bit kernel core/linux-rpi4-mainline-headers 5.4.1-1 [installed] Header files and scripts for building modules for linux kernel - Raspberry Pi 4 64-bit kernel
It is the RPi tree kernel with all of the current upstream code. I have been testing the 5.4.0-rc8 kernel for about a week and not run into any issues. I ran a few tests this mourning with the 5.4.1 in the repo and all seems to be still ok.
Be advised it will overwrite your /boot/config.txt and cmdline.txt files but will back them up if you have special settings you need to get to. Example: mine would not boot because of special monitor settings because of not getting EDID info and I have the rootfs on a USB 3.0 drive.
There are very few dropped frames playing this 1920x1280 30fps video with out any overclocking just like the 4.19 kernel:
Here I did the same video but overclocked the cpu to 1800 and it only had 1 dropped frame at the same point in the video. I am not recommending overclock and if you do so it is at your own risk but if you do I highly recommend a proper way of cooling with heat sinks and fan.
My config.txt additions:
over_voltage=2 arm_freq=1800 gpu_freq=500 v3d_freq=500