See the commit message in the patch:
Before this patch, hotplugging only worked to replace drives (if you
tried to plug a drive into a SATA port that no drive was plugged in to
at boot, it wouldn't be detected) and you'd have to manually rescan
the bus (echo "- - -" > /sys/class/scsi_host/host*/scan) to make
plugs/unplugs get detected by the operating system.
Now, hotplugging works for all ports (tested and working on Supermicro
X11SSH-LN4F) and there's no need to manually rescan (it sometimes
takes a few seconds for unplugs to be detected, but plugs are detected
instantly).
Also submitted upstream as https://review.coreboot.org/c/coreboot/+/91824
Ron Nazarov