Re: [PATCH RFC 00/10] riscv: Add support for rva23

[Paul Walmsley <pjw@kernel.org>]

Hi Charlie,

On Wed, 10 Dec 2025, Charlie Jenkins wrote:

> I will be talking about rva23 at Plumbers this year and have this series
> as a draft of my ideas.
> 
> rva23 is a RVI profile to group together extensions that are expected to
> be found on high-performance systems.
> 
> This series:
> 1. Introduces a framework to add extensions to the kernel cflags
> 2. Adds a rva23 config option 
> 3. Optimizes riscv_has_extension_*
> 
> This is based on 6.18 plus
> https://lore.kernel.org/linux-riscv/20251020-riscv-altn-helper-wip-v4-0-ef941c87669a@iscas.ac.cn/.
> 
> Signed-off-by: Charlie Jenkins <thecharlesjenkins@gmail.com>

Thanks for sending these.  A few suggestions, for when you resend these 
patches:

- Please split the cleanup patches into a separate, predecessor series 
  from the patches that are designed to change the way that extensions are 
  handled.  The latter patches will probably take longer to reach 
  consensus around.

- Probably best not to characterize the latter set of patches as "RVA23 
  support" patches, since they won't affect the kernel's ability to 
  support RVA23.  These just enable building an RVA23-specific kernel.  
  It's not entirely clear to me that this is a win -- I assume the 
  argument would be that the performance benefit for some systems would 
  justify the additional complexity and the performance reduction for 
  other systems? -- but that's what we'd need to discuss.

- Continuing that line of thinking, I think we'd want to see some 
  performance measurements after these patches are applied, on 
  hardware, for both RVA23-specific kernels and non-RVA23-specific 
  kernels, and the latter on both non-RVA23 hardware and RVA23 hardware.


thanks,

- Paul

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