Re: [PATCH v5 03/17] riscv: vector: Use vlenb from DT

Conor Dooley
2024-05-03T16:59:40Z

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On Thu, May 02, 2024 at 09:46:38PM -0700, Charlie Jenkins wrote:
> If vlenb is provided in the device tree, prefer that over reading the
> vlenb csr.
>
> Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> ---
> arch/riscv/include/asm/cpufeature.h | 2 ++
> arch/riscv/kernel/cpufeature.c | 43 +++++++++++++++++++++++++++++++++++++
> arch/riscv/kernel/vector.c | 12 ++++++++++-
> 3 files changed, 56 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index 347805446151..0c4f08577015 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -31,6 +31,8 @@ DECLARE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
> /* Per-cpu ISA extensions. */
> extern struct riscv_isainfo hart_isa[NR_CPUS];
>
> +extern u32 riscv_vlenb_of;
> +
> void riscv_user_isa_enable(void);
>
> #if defined(CONFIG_RISCV_MISALIGNED)
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 3ed2359eae35..12c79db0b0bb 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -35,6 +35,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
> /* Per-cpu ISA extensions. */
> struct riscv_isainfo hart_isa[NR_CPUS];
>
> +u32 riscv_vlenb_of;
> +
> /**
> * riscv_isa_extension_base() - Get base extension word
> *
> @@ -648,6 +650,42 @@ static int __init riscv_isa_fallback_setup(char *__unused)
> early_param("riscv_isa_fallback", riscv_isa_fallback_setup);
> #endif
>
> +static int has_riscv_homogeneous_vlenb(void)
> +{
> + int cpu;
> + u32 prev_vlenb = 0;
> + u32 vlenb;
> +
> + for_each_possible_cpu(cpu) {
> + struct device_node *cpu_node;
> +
> + cpu_node = of_cpu_device_node_get(cpu);
> + if (!cpu_node) {
> + pr_warn("Unable to find cpu node\n");
> + return -ENOENT;
> + }
> +
> + if (of_property_read_u32(cpu_node, "riscv,vlenb", &vlenb)) {
> + of_node_put(cpu_node);
> +
> + if (prev_vlenb)
> + return -ENOENT;
> + continue;
> + }
> +
> + if (prev_vlenb && vlenb != prev_vlenb) {
> + of_node_put(cpu_node);
> + return -ENOENT;
> + }
> +
> + prev_vlenb = vlenb;
> + of_node_put(cpu_node);
> + }
> +
> + riscv_vlenb_of = vlenb;
> + return 0;
> +}
> +
> void __init riscv_fill_hwcap(void)
> {
> char print_str[NUM_ALPHA_EXTS + 1];
> @@ -671,6 +709,11 @@ void __init riscv_fill_hwcap(void)
> pr_info("Falling back to deprecated \"riscv,isa\"\n");
> riscv_fill_hwcap_from_isa_string(isa2hwcap);
> }
> +
> + if (elf_hwcap & COMPAT_HWCAP_ISA_V && has_riscv_homogeneous_vlenb() < 0) {

I still think this isn't quite right, as it will emit a warning when
RISCV_ISA_V is disabled. The simplest thing to do probably is just
add an `if (IS_ENABLED(CONFIG_RISCV_ISA_V) return 0` shortcut the to
function? It'll get disabled a few lines later so I think a zero is
safe.

> + pr_warn("Unsupported heterogeneous vlen detected, vector extension disabled.\n");
> + elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
> + }
> }
>
> /*
> diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
> index 6727d1d3b8f2..e04586cdb7f0 100644
> --- a/arch/riscv/kernel/vector.c
> +++ b/arch/riscv/kernel/vector.c
> @@ -33,7 +33,17 @@ int riscv_v_setup_vsize(void)
> {
> unsigned long this_vsize;
>
> - /* There are 32 vector registers with vlenb length. */
> + /*
> + * There are 32 vector registers with vlenb length.
> + *
> + * If the riscv,vlenb property was provided by the firmware, use that
> + * instead of probing the CSRs.
> + */
> + if (riscv_vlenb_of) {
> + this_vsize = riscv_vlenb_of * 32;
> + return 0;
> + }
> +
> riscv_v_enable();
> this_vsize = csr_read(CSR_VLENB) * 32;
> riscv_v_disable();
>
> --
> 2.44.0
>

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