forked from Mirrors/opensbi

T-Head developers surely have a different understanding of time CSR and CLINT's mtime register with SiFive ones, that they did not implement the mtime register at all -- as shown in openC906 source code, their time CSR value is just exposed at the top of their processor IP block and expects an external continous counter, which makes it not overrideable, and thus mtime register is not implemented, even not for reading. However, if CLINTEE is not enabled in T-Head's MXSTATUS extended CSR, these systems still rely on the mtimecmp registers to generate timer interrupts. This makes it necessary to implement T-Head C9xx CLINT support in OpenSBI MTIMER driver, which skips implementing reading mtime register and falls back to default code that reads time CSR. Add a quirk into MTIMER driver, which represents a mtime register is lacking and time CSR value should be used instead. Signed-off-by: Icenowy Zheng <uwu@icenowy.me> Reviewed-by: Anup Patel <anup@brainfault.org>