Re: [RFC 0/2] RISC-V: A proposal to add vendor-specific code

[Palmer Dabbelt]

On Mon, 05 Nov 2018 00:52:52 PST (-0800), Arnd Bergmann wrote:
> On 11/5/18, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> > On Mon, Nov 05, 2018 at 02:58:07PM +0800, Vincent Chen wrote:
> > > Many thanks for kinds of comments. I quickly synthesize the comments and
> > > list them as below.
> > > 1. The kernel image shall include all vendor-specific code.
> >
> > I fundamentally disagree with thisâ and think it should be the contrary.
> >
> > 1. The kernel shall support no vendor specific instructions whatsoever,
> > period.
>
> I think what was meant above is
>
> 1. If a vendor extension requires kernel support, that support
> must be able to be built into a kernel image without breaking support
> for CPUs that do not have that extension, to allow building a single
> kernel image that works on all CPUs.

Yes.  I don't want anything that won't compile with upstream GCC, but I also 
don't want to have a Kconfig that says "make the kernel only work on $VENDOR's 
implementation".  I think this can be achieved, at least for the cases I've 
seen so far.