firmware: Not to clear all the MIP

In generic behavior of QEMU, if the pending bits of PLIC are still set and
we clear the SEIP, the QEMU may not set the SEIP back immediately and the
interrupt may not be handled anymore until the new interrupts arrived and
QEMU set the SEIP back which is a generic behavior in QEMU.

Signed-off-by: Nick Hu <nick.hu@sifive.com>
Signed-off-by: Jim Shu <jim.shu@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>

diff --git a/firmware/fw_base.S b/firmware/fw_base.S
index fb6ac92..ceef44f 100644 (file)
--- a/firmware/fw_base.S
+++ b/firmware/fw_base.S
@@ -428,9 +428,15 @@ _start_warm:
        li      ra, 0
        call    _reset_regs
 
-       /* Disable and clear all interrupts */
+       /* Disable all interrupts */
        csrw    CSR_MIE, zero
-       csrw    CSR_MIP, zero
+       /*
+        * Only clear the MIP_SSIP and MIP_STIP. For the platform like QEMU,
+        * If we clear other interrupts like MIP_SEIP and the pendings of
+        * PLIC still exist, the QEMU may not set it back immediately.
+        */
+       li      t0, (MIP_SSIP | MIP_STIP)
+       csrc    CSR_MIP, t0
 
        /* Find HART count and HART stack size */
        lla     a4, platform