Re: [PATCH v3 04/17] riscv: vector: Use vlenb from DT

[Conor Dooley <conor@kernel.org>]

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On Fri, Apr 26, 2024 at 04:17:52PM +0100, Conor Dooley wrote:
> On Sat, Apr 20, 2024 at 06:04:36PM -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      | 26 ++++++++++++++++++++++++++
> >  arch/riscv/kernel/vector.c          | 13 +++++++++----
> >  3 files changed, 37 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> > index 347805446151..809f61ffb667 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_dt[NR_CPUS];
> > +
> >  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 c6e27b45e192..48874aac4871 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_dt[NR_CPUS];
> > +
> >  /**
> >   * riscv_isa_extension_base() - Get base extension word
> >   *
> > @@ -656,6 +658,28 @@ static int __init riscv_isa_fallback_setup(char *__unused)
> >  early_param("riscv_isa_fallback", riscv_isa_fallback_setup);
> >  #endif
> >  
> > +static void riscv_set_vlenb_from_dt(void)
> 
> I'd expect to see a name here that had "of" in it, not "dt".

Also, "set" - I think "get" is more suitable here given that this
doesn't actually set the vlen, we only do any setting later on in
riscv_v_set_vsize().

> 
> > +{
> > +	int cpu;
> > +
> > +	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");
> > +			continue;
> > +		}
> > +
> > +		if (!of_property_read_u32(cpu_node, "riscv,vlenb", &riscv_vlenb_dt[cpu])) {
> > +			of_node_put(cpu_node);
> > +			continue;
> > +		}
> > +
> > +		of_node_put(cpu_node);
> > +	}
> > +}
> > +
> >  void __init riscv_fill_hwcap(void)
> >  {
> >  	char print_str[NUM_ALPHA_EXTS + 1];
> > @@ -675,6 +699,8 @@ void __init riscv_fill_hwcap(void)
> >  	} else {
> >  		int ret = riscv_fill_hwcap_from_ext_list(isa2hwcap);
> >  
> > +		riscv_set_vlenb_from_dt();
> 
> Hmm, I think we can go a step further here. We know all of the CPUs
> widths by the time we get to the first call to riscv_v_setup_vsize(), can
> we examine the whole list and decide not to enable vector if they do
> not match, rather than continuing and failing to online CPUs that having
> the mismatched size?
> 
> I guess that can go into the `if (elf_hwcap & COMPAT_HWCAP_ISA_V)`
> condition we already have, and would require clearing the bit from the
> mask we have at the moment.
> 
> Cheers,
> Conor.
> 
> > +
> >  		if (ret && riscv_isa_fallback) {
> >  			pr_info("Falling back to deprecated \"riscv,isa\"\n");
> >  			riscv_fill_hwcap_from_isa_string(isa2hwcap);
> > diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
> > index 6727d1d3b8f2..fb7f3ca80d9e 100644
> > --- a/arch/riscv/kernel/vector.c
> > +++ b/arch/riscv/kernel/vector.c
> > @@ -32,11 +32,16 @@ EXPORT_SYMBOL_GPL(riscv_v_vsize);
> >  int riscv_v_setup_vsize(void)
> >  {
> >  	unsigned long this_vsize;
> > +	int cpu = smp_processor_id();
> >  
> > -	/* There are 32 vector registers with vlenb length. */
> > -	riscv_v_enable();
> > -	this_vsize = csr_read(CSR_VLENB) * 32;
> > -	riscv_v_disable();
> > +	if (riscv_vlenb_dt[cpu]) {
> > +		this_vsize = riscv_vlenb_dt[cpu];
> 
> > +	} else {
> > +		/* There are 32 vector registers with vlenb length. */
> > +		riscv_v_enable();
> > +		this_vsize = csr_read(CSR_VLENB) * 32;
> > +		riscv_v_disable();
> > +	}
> >  
> >  	if (!riscv_v_vsize) {
> >  		riscv_v_vsize = this_vsize;
> > 
> > -- 
> > 2.44.0
> > 



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