Re: [RFC PATCH 06/11] target/riscv: Update CSR xtvec in CLIC mode

[Frank Chang <frank.chang@sifive.com>]

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LIU Zhiwei <zhiwei_liu@c-sky.com> 於 2021年4月9日 週五 下午3:51寫道：

> The new CLIC interrupt-handling mode is encoded as a new state in the
> existing WARL xtvec register, where the low two bits of are 11.
>
> Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
> ---
>  target/riscv/csr.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/csr.c b/target/riscv/csr.c
> index f6c84b9fe4..39ff72041a 100644
> --- a/target/riscv/csr.c
> +++ b/target/riscv/csr.c
> @@ -637,9 +637,18 @@ static int read_mtvec(CPURISCVState *env, int csrno,
> target_ulong *val)
>
>  static int write_mtvec(CPURISCVState *env, int csrno, target_ulong val)
>  {
> -    /* bits [1:0] encode mode; 0 = direct, 1 = vectored, 2 >= reserved */
> +    /*
> +     * bits [1:0] encode mode; 0 = direct, 1 = vectored, 3 = CLIC,
> +     * others reserved
> +     */
>      if ((val & 3) < 2) {
>          env->mtvec = val;
>

We might need to zero new fields in mcause when set back to basic mode:

Section 4.7:
When basic mode is written to xtvec,
the new xcause state fields (mhinv and mpil) are zeroed.
The other new xcause fields, mpp and mpie, appear as zero in the xcause CSR
but the corresponding state bits in the mstatus register are not cleared.


> +    } else if ((val & 1) && env->clic) {
> +        /*
> +         * If only CLIC mode is supported, writes to bit 1 are also
> ignored and
> +         * it is always set to one. CLIC mode hardwires xtvec bits 2-5 to
> zero.
> +         */
> +        env->mtvec = ((val & ~0x3f) << 6) | (0b000011);
>      } else {
>          qemu_log_mask(LOG_UNIMP, "CSR_MTVEC: reserved mode not
> supported\n");
>      }
> @@ -837,9 +846,18 @@ static int read_stvec(CPURISCVState *env, int csrno,
> target_ulong *val)
>
>  static int write_stvec(CPURISCVState *env, int csrno, target_ulong val)
>  {
> -    /* bits [1:0] encode mode; 0 = direct, 1 = vectored, 2 >= reserved */
> +    /*
> +     * bits [1:0] encode mode; 0 = direct, 1 = vectored, 3 = CLIC,
> +     * others reserved
> +     */
>      if ((val & 3) < 2) {
>          env->stvec = val;
>

Same to write_mtvec()

Regards,
Frank Chang


> +    } else if ((val & 1) && env->clic) {
> +        /*
> +         * If only CLIC mode is supported, writes to bit 1 are also
> ignored and
> +         * it is always set to one. CLIC mode hardwires xtvec bits 2-5 to
> zero.
> +         */
> +        env->stvec = ((val & ~0x3f) << 6) | (0b000011);
>      } else {
>          qemu_log_mask(LOG_UNIMP, "CSR_STVEC: reserved mode not
> supported\n");
>      }
> --
> 2.25.1
>
>
>

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