Re: [PATCH v4 05/16] riscv: Extend cpufeature.c to detect vendor extensions

Charlie Jenkins
2024-05-01T17:05:02Z

On Wed, May 01, 2024 at 11:46:07AM +0100, Conor Dooley wrote:
> On Fri, Apr 26, 2024 at 02:29:19PM -0700, Charlie Jenkins wrote:
> > Separate vendor extensions out into one struct per vendor
> > instead of adding vendor extensions onto riscv_isa_ext.
> >
> > Add a hidden config RISCV_ISA_VENDOR_EXT to conditionally include this
> > code.
> >
> > The xtheadvector vendor extension is added using these changes.
>
> This mostly looks good to me, thanks for the updates. There's one thing
> that I think is wrong, but I need to test and will get back to you on...
>
> > Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
> > ---
> > arch/riscv/Kconfig | 2 +
> > arch/riscv/Kconfig.vendor | 19 ++++++
> > arch/riscv/include/asm/cpufeature.h | 18 ++++++
> > arch/riscv/include/asm/vendor_extensions.h | 26 ++++++++
> > arch/riscv/include/asm/vendor_extensions/thead.h | 19 ++++++
> > arch/riscv/kernel/Makefile | 2 +
> > arch/riscv/kernel/cpufeature.c | 77 ++++++++++++++++++------
> > arch/riscv/kernel/vendor_extensions.c | 18 ++++++
> > arch/riscv/kernel/vendor_extensions/Makefile | 3 +
> > arch/riscv/kernel/vendor_extensions/thead.c | 36 +++++++++++
> > 10 files changed, 200 insertions(+), 20 deletions(-)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index be09c8836d56..fec86fba3acd 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -759,6 +759,8 @@ config RISCV_EFFICIENT_UNALIGNED_ACCESS
> >
> > endchoice
> >
> > +source "arch/riscv/Kconfig.vendor"
> > +
> > endmenu # "Platform type"
> >
> > menu "Kernel features"
> > diff --git a/arch/riscv/Kconfig.vendor b/arch/riscv/Kconfig.vendor
> > new file mode 100644
> > index 000000000000..4fc86810af1d
> > --- /dev/null
> > +++ b/arch/riscv/Kconfig.vendor
> > @@ -0,0 +1,19 @@
> > +menu "Vendor extensions"
> > +
> > +config RISCV_ISA_VENDOR_EXT
> > + bool
> > +
> > +menu "T-Head"
> > +config RISCV_ISA_VENDOR_EXT_THEAD
> > + bool "T-Head vendor extension support"
> > + select RISCV_ISA_VENDOR_EXT
> > + default y
> > + help
> > + Say N here if you want to disable all T-Head vendor extension
> > + support. This will cause any T-Head vendor extensions that are
> > + requested to be ignored.
>
> What does "requested to be ignored" mean to a punter configuring a
> kernel? I'd expect this to be something like:
>
> "Say N here to disable detection of and support for all T-Head vendor
> extensions. Without this option enabled, T-Head vendor extensions will
> not be detected at boot and their presence not reported to userspace."

Sounds great I will change to that.

- Charlie

>
> In general, I'd expect something that needs some support in the kernel
> (like vector) to function to have a dedicated option, but the likes of
> their Zba variant could be detected and reported via hwprobe et al
> once RISCV_ISA_VENDOR_EXT_THEAD is enabled.
>
> Cheers,
> Conor.