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SubjectRe: [PATCH v8 24/25] powerpc: Adopt nvram module for PPC64
On Sat, 29 Dec 2018, Arnd Bergmann wrote:

> On Wed, Dec 26, 2018 at 1:43 AM Finn Thain <fthain@telegraphics.com.au> wrote:
>
> > +static ssize_t ppc_nvram_get_size(void)
> > +{
> > + if (ppc_md.nvram_size)
> > + return ppc_md.nvram_size();
> > + return -ENODEV;
> > +}
>
> > +const struct nvram_ops arch_nvram_ops = {
> > + .read = ppc_nvram_read,
> > + .write = ppc_nvram_write,
> > + .get_size = ppc_nvram_get_size,
> > + .sync = ppc_nvram_sync,
> > +};
>
> Coming back to this after my comment on the m68k side, I notice that
> there is now a double indirection through function pointers. Have you
> considered completely removing the operations from ppc_md instead by
> having multiple copies of nvram_ops?
>

I considered a few alternatives. I figured that it was refactoring that
could be deferred, as it would be confined to arch/powerpc. I was more
interested in the cross-platform API.

> With the current method, it does seem odd to have a single
> per-architecture instance of the exported structure containing function
> pointers. This doesn't give us the flexibility of having multiple copies
> in the kernel the way that ppc_md does, but it adds overhead compared to
> simply exporting the functions directly.
>

You're right, there is overhead here.

With a bit of auditing, wrappers like the one you quoted (which merely
checks whether or not a ppc_md method is implemented) could surely be
avoided.

The arch_nvram_ops methods are supposed to optional (that is, they are
allowed to be NULL).

We could call exactly the same function pointers though either ppc_md or
arch_nvram_ops. That would avoid the double indirection.

--

> Arnd
>

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