Re: [PATCH 05/13] riscv: vector: Use vlenb from DT for thead

[Jessica Clarke <jrtc27@jrtc27.com>]

On 10 Jun 2024, at 05:45, Charlie Jenkins <charlie@rivosinc.com> wrote:
> 
> If thead,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      | 48 +++++++++++++++++++++++++++++++++++++
> arch/riscv/kernel/vector.c          | 12 +++++++++-
> 3 files changed, 61 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index b029ca72cebc..e0a3164c7a06 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 thead_vlenb_of;
> +
> void riscv_user_isa_enable(void);
> 
> #define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size) { \
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 2107c59575dd..0c01f33f2348 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -37,6 +37,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
> /* Per-cpu ISA extensions. */
> struct riscv_isainfo hart_isa[NR_CPUS];
> 
> +u32 thead_vlenb_of;
> +
> /**
>  * riscv_isa_extension_base() - Get base extension word
>  *
> @@ -625,6 +627,46 @@ static void __init riscv_fill_vendor_ext_list(int cpu)
> }
> }
> 
> +static int has_thead_homogeneous_vlenb(void)
> +{
> + int cpu;
> + u32 prev_vlenb = 0;
> + u32 vlenb;
> +
> + /* Ignore vlenb if vector is not enabled in the kernel */
> + if (!IS_ENABLED(CONFIG_RISCV_ISA_V))

It’s not V though. You probably want to split out “vector” from “V” in
Kconfig land. Most places want the former, I assume, but some want the
latter.

Jess

> + return 0;
> +
> + 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, "thead,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);
> + }
> +
> + thead_vlenb_of = vlenb;
> + return 0;
> +}
> +
> static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
> {
> unsigned int cpu;
> @@ -689,6 +731,12 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
> riscv_fill_vendor_ext_list(cpu);
> }
> 
> + if (riscv_isa_vendor_extension_available(THEAD_VENDOR_ID, XTHEADVECTOR) &&
> +    has_thead_homogeneous_vlenb() < 0) {
> + pr_warn("Unsupported heterogeneous vlenb detected, vector extension disabled.\n");
> + elf_hwcap &= ~COMPAT_HWCAP_ISA_V;
> + }
> +
> if (bitmap_empty(riscv_isa, RISCV_ISA_EXT_MAX))
> return -ENOENT;
> 
> diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
> index 6727d1d3b8f2..3ba2f2432483 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 thead,vlenb property was provided by the firmware, use that
> + * instead of probing the CSRs.
> + */
> + if (thead_vlenb_of) {
> + this_vsize = thead_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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