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

[Charlie Jenkins <charlie@rivosinc.com>]

On Mon, Jun 10, 2024 at 06:51:56PM +0100, Jessica Clarke wrote:
> 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.

There is the xtheadvector kconfig that is introduced later in this
series in the "riscv: vector: Support xtheadvector save/restore" patch.
I think I should shuffle the code in these patches around so I can use
CONFIG_RISCV_ISA_XTHEADVECTOR here instead.

- Charlie

> 
> 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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