On Wed, Apr 25, 2018 at 4:56 PM Michael Clark <m...@sifive.com> wrote:
> satp is WARL so it should not trap on illegal writes, rather
> it can be hardwired to zero and silently ignore illegal writes.
> It seems the RISC-V WARL behaviour is preferred to having to
> trap overhead versus simply reading back the value and checking
> if the write took (saves hundreds of cycles and more complex
> trap handling code).
> Cc: Sagar Karandikar <sag...@eecs.berkeley.edu>
> Cc: Bastian Koppelmann <kbast...@mail.uni-paderborn.de>
> Cc: Palmer Dabbelt <pal...@sifive.com>
> Cc: Alistair Francis <alistair.fran...@wdc.com>
> Signed-off-by: Michael Clark <m...@sifive.com>
Reviewed-by: Alistair Francis <alistair.fran...@wdc.com>
Alistair
> ---
> target/riscv/op_helper.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
> diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
> index 7c6068b..101dac1 100644
> --- a/target/riscv/op_helper.c
> +++ b/target/riscv/op_helper.c
> @@ -255,7 +255,7 @@ void csr_write_helper(CPURISCVState *env,
target_ulong val_to_write,
> }
> case CSR_SATP: /* CSR_SPTBR */ {
> if (!riscv_feature(env, RISCV_FEATURE_MMU)) {
> - goto do_illegal;
> + break;
> }
> if (env->priv_ver <= PRIV_VERSION_1_09_1 && (val_to_write ^
env->sptbr))
> {
> @@ -465,7 +465,10 @@ target_ulong csr_read_helper(CPURISCVState *env,
target_ulong csrno)
> return env->scounteren;
> case CSR_SCAUSE:
> return env->scause;
> - case CSR_SPTBR:
> + case CSR_SATP: /* CSR_SPTBR */
> + if (!riscv_feature(env, RISCV_FEATURE_MMU)) {
> + return 0;
> + }
> if (env->priv_ver >= PRIV_VERSION_1_10_0) {
> return env->satp;
> } else {
> --
> 2.7.0
