[PATCH 2/2] lib: sbi_illegal_insn: Add emulation for fence.tso

[Anup Patel]

On Sun, May 29, 2022 at 11:55 PM Samuel Holland <samuel at sholland.org> wrote:
>
> While OpenC906 appears to properly decode `fence.tso` as a fence
> instruction[1], the version of the C906 taped out in the Allwinner D1
> does not, and raises illegal instruction.
>
> Handle this errata by emulating `fence.tso` as `fence rw, rw`.
>
> [1]: https://github.com/T-head-Semi/openc906/blob/30827e7f/C906_RTL_FACTORY/gen_rtl/idu/rtl/aq_idu_id_decd.v#L2097
>
> Signed-off-by: Samuel Holland <samuel at sholland.org>
> ---
>
>  lib/sbi/sbi_illegal_insn.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/lib/sbi/sbi_illegal_insn.c b/lib/sbi/sbi_illegal_insn.c
> index 39ef990..44c9385 100644
> --- a/lib/sbi/sbi_illegal_insn.c
> +++ b/lib/sbi/sbi_illegal_insn.c
> @@ -8,6 +8,7 @@
>   */
>
>  #include <sbi/riscv_asm.h>
> +#include <sbi/riscv_barrier.h>
>  #include <sbi/riscv_encoding.h>
>  #include <sbi/sbi_bitops.h>
>  #include <sbi/sbi_emulate_csr.h>
> @@ -32,6 +33,17 @@ static int truly_illegal_insn(ulong insn, struct sbi_trap_regs *regs)
>         return sbi_trap_redirect(regs, &trap);
>  }
>
> +static int misc_mem_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
> +{
> +       /* Errata workaround: emulate `fence.tso` as `fence rw, rw`. */
> +       if (insn == 0x8330000fUL) {

Instead of hard-coding "fence.tso" encoding, I suggest to add match
and mask defines in riscv_encoding.h.

Something like this:
#define INSN_MATCH_FENCE_TSO 0x8330000f
#define INSN_MASK_FENCE_TSO 0xffffffff

> +               smp_mb();
> +               return 0;
> +       }
> +
> +       return truly_illegal_insn(insn, regs);
> +}
> +
>  static int system_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
>  {
>         int do_write, rs1_num = (insn >> 15) & 0x1f;
> @@ -84,7 +96,7 @@ static const illegal_insn_func illegal_insn_table[32] = {
>         truly_illegal_insn, /* 0 */
>         truly_illegal_insn, /* 1 */
>         truly_illegal_insn, /* 2 */
> -       truly_illegal_insn, /* 3 */
> +       misc_mem_opcode_insn, /* 3 */
>         truly_illegal_insn, /* 4 */
>         truly_illegal_insn, /* 5 */
>         truly_illegal_insn, /* 6 */
> --
> 2.35.1
>
>
> --
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Apart from a minor comment above, this looks good to me.

Reviewed-by: Anup Patel <anup at brainfault.org>

Regards,
Anup