Re: [PATCH v2 2/9] RISC-V: Detect XVentanaCondOps from ISA string

[Charlie Jenkins <charlie@rivosinc.com>]

On Mon, Sep 25, 2023 at 10:48:11AM -0700, Charlie Jenkins wrote:
> On Mon, Sep 25, 2023 at 07:08:52PM +0530, Anup Patel wrote:
> > The Veyron-V1 CPU supports custom conditional arithmetic and
> > conditional-select/move operations referred to as XVentanaCondOps
> > extension. In fact, QEMU RISC-V also has support for emulating
> > XVentanaCondOps extension.
> > 
> > Let us detect XVentanaCondOps extension from ISA string available
> > through DT or ACPI.
> > 
> > Signed-off-by: Anup Patel <apatel@ventanamicro.com>
> > Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> > ---
> >  arch/riscv/include/asm/hwcap.h | 1 +
> >  arch/riscv/kernel/cpufeature.c | 1 +
> >  2 files changed, 2 insertions(+)
> > 
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index 0f520f7d058a..b7efe9e2fa89 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -59,6 +59,7 @@
> >  #define RISCV_ISA_EXT_ZIFENCEI		41
> >  #define RISCV_ISA_EXT_ZIHPM		42
> >  #define RISCV_ISA_EXT_SMSTATEEN		43
> > +#define RISCV_ISA_EXT_XVENTANACONDOPS	44
> >  
> >  #define RISCV_ISA_EXT_MAX		64
> >  
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index 3755a8c2a9de..3a31d34fe709 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -182,6 +182,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
> >  	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
> >  	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
> >  	__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> > +	__RISCV_ISA_EXT_DATA(xventanacondops, RISCV_ISA_EXT_XVENTANACONDOPS),
> >  };
> >  
> >  const size_t riscv_isa_ext_count = ARRAY_SIZE(riscv_isa_ext);
> > -- 
> > 2.34.1
> > 
> > 
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> 
> I worry about storing vendor extensions in this file. Because vendor
> extensions are not standardized, they can only be expected to have the
> desired behavior on hardware with the appropriate vendor id. A couple
> months ago I sent a patch to address this by handling vector extensions
> independently for each vendor [1]. I dropped the patch because it
> relied upon Heiko's T-Head vector extension support that he stopped
> working on. However, I can revive this patch so you can build off of it.
> 
> This scheme has the added benefit that vendors do not have to worry
> about conficting extensions, and the kernel does not have to act as a
> key registry for vendors.
> 
> What are your thoughts?
> 
> - Charlie
> 
> [1] https://lore.kernel.org/lkml/20230705-thead_vendor_extensions-v1-2-ad6915349c4d@rivosinc.com/
> 

I guess I don't need to revive the patch, you could just take the code
and update it for xventanacondops.

- Charlie