Hi!
[ Upstream commit 1d4df649cbb4b26d19bea38ecff4b65b10a1bbca ]
The thead,c900-plic has been used in opensbi to distinguish PLIC [1]. Although PLICs have the same behaviors in Linux, they are different hardware with some custom initializing in firmware(opensbi).
Qute opensbi patch commit-msg by Samuel:
The T-HEAD PLIC implementation requires setting a delegation bit to allow access from S-mode. Now that the T-HEAD PLIC has its own compatible string, set this bit automatically from the PLIC driver, instead of reaching into the PLIC's MMIO space from another driver.
The "thead,c900-plic" string is added into single place in the kernel. This means that a) it will probably not do anything useful in -stable kernels and b) it is certainly missing documentation etc.
In mainline, string is documented in Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
Best regards, Pavel