[PATCH 2/2] lib: sbi: Handle the case were MTVAL has illegal instruction address

[Heinrich Schuchardt]

On 8/15/20 7:00 PM, Anup Patel wrote:
> The Kendryte K210 follows RISC-V v1.9 spec so MTVAL has instruction
> address (instead of instruction encoding) on illegal instruction trap.
>
> To handle above case, we fix sbi_illegal_insn_handler() without any
> impact on RISC-V v1.10 (or higher) systems. This achieved by exploiting
> the fact that program counter (and instruction address) is always 2-byte
> aligned in RISC-V world.
>
> Signed-off-by: Anup Patel <anup.patel at wdc.com>

On the Sipeed Maixduino (Kendryte K210) this resolves the problem of
handling rdtime in S-mode U-Boot.

Tested-by: Heinrich Schuchardt <xypron.glpk at gmx.de>

> ---
>  lib/sbi/sbi_illegal_insn.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/lib/sbi/sbi_illegal_insn.c b/lib/sbi/sbi_illegal_insn.c
> index 0e5523f..779a727 100644
> --- a/lib/sbi/sbi_illegal_insn.c
> +++ b/lib/sbi/sbi_illegal_insn.c
> @@ -118,13 +118,22 @@ int sbi_illegal_insn_handler(ulong insn, struct sbi_trap_regs *regs)
>  {
>  	struct sbi_trap_info uptrap;
>
> +	/*
> +	 * We only deal with 32bit (or longer) illegal instructions. If we
> +	 * see instruction is zero OR instruction is 16bit then we fetch and
> +	 * check the instruction encoding using unprivilege access.
> +	 *
> +	 * The program counter (PC) in RISC-V world is always 2-byte aligned
> +	 * so handling only 32bit (or longer) illegal instructions also help
> +	 * the case where MTVAL CSR contains instruction address for illegal
> +	 * instruction trap.
> +	 */
> +
>  	if (unlikely((insn & 3) != 3)) {
> -		if (insn == 0) {
> -			insn = sbi_get_insn(regs->mepc, &uptrap);
> -			if (uptrap.cause) {
> -				uptrap.epc = regs->mepc;
> -				return sbi_trap_redirect(regs, &uptrap);
> -			}
> +		insn = sbi_get_insn(regs->mepc, &uptrap);
> +		if (uptrap.cause) {
> +			uptrap.epc = regs->mepc;
> +			return sbi_trap_redirect(regs, &uptrap);
>  		}
>  		if ((insn & 3) != 3)
>  			return truly_illegal_insn(insn, regs);
>