CSR_STFILL
sfb_state = (csr_read32(LOONGARCH_CSR_IMPCTL1) & CSR_STFILL) >> CSR_STFILL_SHIFT;
csr_xchg32(val, CSR_STFILL, LOONGARCH_CSR_IMPCTL1);
state = (csr_read32(LOONGARCH_CSR_IMPCTL1) & CSR_STFILL) >> CSR_STFILL_SHIFT;