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

[Charlie Jenkins <charlie@rivosinc.com>]

On Fri, Apr 26, 2024 at 05:21:16PM +0100, Conor Dooley wrote:
> 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.

Good point, thank you. Since this is not supported with ACPI, I will
clear the COMPAT_HWCAP_ISA_V bit from elf_hwcap if
riscv_set_vlenb_from_dt() (which will be renamed) determines that the
the riscv,vlenb field changes between CPU entries. 

- Charlie

> > 
> > 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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