RISC-V: Allow interrupt controllers to claim interrupts

We can't allow the supervisor to control SEIP as this would allow the
supervisor to clear a pending external interrupt which will result in
lost a interrupt in the case a PLIC is attached. The SEIP bit must be
hardware controlled when a PLIC is attached.

This logic was previously hard-coded so SEIP was always masked even
if no PLIC was attached. This patch adds riscv_cpu_claim_interrupts
so that the PLIC can register control of SEIP. In the case of models
without a PLIC (spike), the SEIP bit remains software controlled.

This interface allows for hardware control of supervisor timer and
software interrupts by other interrupt controller models.

Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Sagar Karandikar <sagark@eecs.berkeley.edu>
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Cc: Alistair Francis <Alistair.Francis@wdc.com>
Signed-off-by: Michael Clark <mjc@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

1 files changed, 2 insertions, 8 deletions

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 9a40b4c7ba..385bb38768 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -550,16 +550,10 @@ static int rmw_mip(CPURISCVState *env, int csrno, target_ulong *ret_value,
                    target_ulong new_value, target_ulong write_mask)
 {
     RISCVCPU *cpu = riscv_env_get_cpu(env);
-    target_ulong mask = write_mask & delegable_ints;
+    /* Allow software control of delegable interrupts not claimed by hardware */
+    target_ulong mask = write_mask & delegable_ints & ~env->miclaim;
     uint32_t old_mip;
 
-    /* We can't allow the supervisor to control SEIP as this would allow the
-     * supervisor to clear a pending external interrupt which will result in
-     * lost a interrupt in the case a PLIC is attached. The SEIP bit must be
-     * hardware controlled when a PLIC is attached. This should be an option
-     * for CPUs with software-delegated Supervisor External Interrupts. */
-    mask &= ~MIP_SEIP;
-
     if (mask) {
         qemu_mutex_lock_iothread();
         old_mip = riscv_cpu_update_mip(cpu, mask, (new_value & mask));