Re: [PATCH 1/2] riscv: allow case-insensitive ISA string parsing

[Andrew Jones]

On Wed, Apr 26, 2023 at 07:54:39PM +0100, Conor Dooley wrote:
> (+CC Drew)
> 
> Hey Yangyu,
> 
> One meta-level comment - can you submit this patch + my dt-bindings
> patch as a v2?
> Some comments below.
> 
> On Tue, Apr 25, 2023 at 08:00:15PM +0800, Yangyu Chen wrote:
> > According to RISC-V ISA specification, the ISA naming strings are case
> > insensitive. The kernel docs require the riscv,isa string must be all
> > lowercase to simplify parsing currently. However, this limitation is not
> > consistent with RISC-V ISA Spec.
> 
> Please remove the above and cite ACPI's case-insensitivity as the
> rationale for this change.
> 
> > This patch modifies the ISA string parser in the kernel to support
> > case-insensitive ISA string parsing. It replaces `strncmp` with
> > `strncasecmp`, replaces `islower` with `isalpha`, and wraps the
> > dereferenced char in the parser with `tolower`.
> > 
> > Signed-off-by: Yangyu Chen <cyy@xxxxxxxxxxxx>
> > ---
> >  arch/riscv/kernel/cpu.c        |  6 ++++--
> >  arch/riscv/kernel/cpufeature.c | 20 ++++++++++----------
> >  2 files changed, 14 insertions(+), 12 deletions(-)
> > 
> > diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> > index 8400f0cc9704..531c76079b73 100644
> > --- a/arch/riscv/kernel/cpu.c
> > +++ b/arch/riscv/kernel/cpu.c
> > @@ -4,6 +4,7 @@
> >   */
> >  
> >  #include <linux/cpu.h>
> > +#include <linux/ctype.h>
> >  #include <linux/init.h>
> >  #include <linux/seq_file.h>
> >  #include <linux/of.h>
> > @@ -41,7 +42,7 @@ int riscv_of_processor_hartid(struct device_node *node, unsigned long *hart)
> >  		pr_warn("CPU with hartid=%lu has no \"riscv,isa\" property\n", *hart);
> >  		return -ENODEV;
> >  	}
> > -	if (isa[0] != 'r' || isa[1] != 'v') {
> > +	if (tolower(isa[0]) != 'r' || tolower(isa[1]) != 'v') {
> >  		pr_warn("CPU with hartid=%lu has an invalid ISA of \"%s\"\n", *hart, isa);
> >  		return -ENODEV;
> 
> I don't understand why this is even here in the first place. I'd be
> inclined to advocate for it's entire removal. Checking *only* that there
> is an "rv" in that string seems pointless to me. If you're on a 64-bit
> kernel and the node has riscv,isa = "rv32ima" it's gonna say it is okay?
> Drew what do you think?

It makes some sense to me as a garbage detector. It's unlikely the first
two bytes will be "rv" if the string is random junk. I think it should
also do a strlen(isa) >= 4 check first, though. of_property_read_string()
will succeed even when the string is "".

Thanks,
drew