Re: [PATCH v4 2/4] RISC-V: Add riscv_isa reprensenting ISA features common across CPUs

[Paul Walmsley]

Hi Anup, Atish,

On Fri, 2 Aug 2019, Atish Patra wrote:

> From: Anup Patel <anup.patel@xxxxxxx>
> 
> This patch adds riscv_isa integer to represent ISA features common
> across all CPUs. The riscv_isa is not same as elf_hwcap because
> elf_hwcap will only have ISA features relevant for user-space apps
> whereas riscv_isa will have ISA features relevant to both kernel
> and user-space apps.
> 
> One of the use case is KVM hypervisor where riscv_isa will be used
> to do following operations:
> 
> 1. Check whether hypervisor extension is available
> 2. Find ISA features that need to be virtualized (e.g. floating
>    point support, vector extension, etc.)
> 
> Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
> Signed-off-by: Atish Patra <atish.patra@xxxxxxx>

Do you have any opinions on how this patch might change for the Z-prefix 
extensions?  This bitfield approach probably won't scale, and with the 
EXPORT_SYMBOL(), it might be worth trying to put together a approach that 
would work over the long term?


- Paul