| Message ID | 1524699938-6764-16-git-send-email-mjc@sifive.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, Apr 25, 2018 at 4:56 PM Michael Clark <mjc@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 <sagark@eecs.berkeley.edu> > Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de> > Cc: Palmer Dabbelt <palmer@sifive.com> > Cc: Alistair Francis <Alistair.Francis@wdc.com> > Signed-off-by: Michael Clark <mjc@sifive.com> Reviewed-by: Alistair Francis <alistair.francis@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
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 {
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 <sagark@eecs.berkeley.edu> Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de> Cc: Palmer Dabbelt <palmer@sifive.com> Cc: Alistair Francis <Alistair.Francis@wdc.com> Signed-off-by: Michael Clark <mjc@sifive.com> --- target/riscv/op_helper.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)