hw/intc: riscv_aclint: Fix mtime write for sstc extension

When changing the mtime value, the period of [s|vs]timecmp timers
should also be updated, similar to the period of mtimecmp timer.

The period of the stimecmp timer is the time until the next S-mode
timer IRQ. The value is calculated as "stimecmp - time". [1]
It is equal to "stimecmp - mtime" since the time CSR is a read-only
shadow of the memory-mapped mtime register.
Thus, changing mtime value will update the period of stimecmp timer.

Similarly, the period of vstimecmp timer is calculated as "vstimecmp -
(mtime + htimedelta)" [2], so changing mtime value will update the
period of vstimecmp timer.

[1] RISC-V Priv spec ch 9.1.1. Supervisor Timer (stimecmp) Register
A supervisor timer interrupt becomes pending, as reflected in the STIP
bit in the mip and sip registers whenever time contains a value
greater than or equal to stimecmp.
[2] RISC-V Priv spec ch19.2.1. Virtual Supervisor Timer (vstimecmp) Register
A virtual supervisor timer interrupt becomes pending, as reflected in
the VSTIP bit in the hip register, whenever (time + htimedelta),
truncated to 64 bits, contains a value greater than or equal to
vstimecmp

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250519143518.11086-3-jim.shu@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/hw/intc/riscv_aclint.c b/hw/intc/riscv_aclint.c
index b0139f03f5..4623cfa029 100644
--- a/hw/intc/riscv_aclint.c
+++ b/hw/intc/riscv_aclint.c
@@ -28,6 +28,7 @@
 #include "qemu/module.h"
 #include "hw/sysbus.h"
 #include "target/riscv/cpu.h"
+#include "target/riscv/time_helper.h"
 #include "hw/qdev-properties.h"
 #include "hw/intc/riscv_aclint.h"
 #include "qemu/timer.h"
@@ -240,6 +241,10 @@ static void riscv_aclint_mtimer_write(void *opaque, hwaddr addr,
             riscv_aclint_mtimer_write_timecmp(mtimer, RISCV_CPU(cpu),
                                               mtimer->hartid_base + i,
                                               mtimer->timecmp[i]);
+            riscv_timer_write_timecmp(env, env->stimer, env->stimecmp, 0, MIP_STIP);
+            riscv_timer_write_timecmp(env, env->vstimer, env->vstimecmp,
+                                      env->htimedelta, MIP_VSTIP);
+
         }
         return;
     }