Re: [PATCH v5 1/4] RISC-V: add Zbc extension detection

[Palmer Dabbelt]

On Mon, 12 Jun 2023 14:31:14 PDT (-0700), Conor Dooley wrote:
> Hey Heiko,
>
> On Mon, Jun 12, 2023 at 11:04:39PM +0200, Heiko Stuebner wrote:
> > From: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> >
> > Add handling for Zbc extension.
> >
> > Zbc provides instruction for carry-less multiplication.
> >
> > Signed-off-by: Heiko Stuebner <heiko.stuebner@xxxxxxxx>
> > ---
> >  arch/riscv/Kconfig             | 22 ++++++++++++++++++++++
> >  arch/riscv/include/asm/hwcap.h |  1 +
> >  arch/riscv/kernel/cpu.c        |  1 +
> >  arch/riscv/kernel/cpufeature.c |  1 +
> >  4 files changed, 25 insertions(+)
>
> Plumbing into the hwprobe stuff would be nice, but that's not a
> requirement for getting stuff merged :)

IIRC we talked about this on IRC, but IMO we shouldn't require something 
be user visible for it to be merged in the kernel.

> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index a3d54cd14fca..754cd154eca5 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -523,6 +523,28 @@ config RISCV_ISA_ZBB
> >  
> >  	   If you don't know what to do here, say Y.
> >  
> > +config TOOLCHAIN_HAS_ZBC
> > +	bool
> > +	default y
> > +	depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zbc)
> > +	depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zbc)
> > +	depends on LLD_VERSION >= 150000 || LD_VERSION >= 23900
> > +	depends on AS_IS_GNU
> > +
> > +config RISCV_ISA_ZBC
> > +	bool "Zbc extension support for bit manipulation instructions"
> > +	depends on TOOLCHAIN_HAS_ZBC
> > +	depends on !XIP_KERNEL && MMU
> > +	default y
> > +	help
> > +	   Adds support to dynamically detect the presence of the ZBC
>
> Nit: s/ZBC/Zbc/
>
> Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
>
> Cheers,
> Conor.