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.
> 
> [1]: https://github.com/riscv-software-src/opensbi/commit/78c2b19218bd62653b9fb31623a42ced45f38ea6
>

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
-- 
http://www.livejournal.com/~pavelmachek