Re: [PATCH v2 1/1] PCI: brcmstb: Use BIT() as __GENMASK() is for internal use only

Andy Shevchenko
2021-11-15T14:16:22Z

On Mon, Nov 15, 2021 at 4:01 PM Robin Murphy <robin.murphy@arm.com> wrote:
> On 2021-11-15 11:20, Andy Shevchenko wrote:
> > Use BIT() as __GENMASK() is for internal use only. The rationale
> > of switching to BIT() is to provide better generated code. The
> > GENMASK() against non-constant numbers may produce an ugly assembler
> > code. On contrary the BIT() is simply converted to corresponding shift
> > operation.
>
> FWIW, If you care about code quality and want the compiler to do the
> obvious thing, why not specify it as the obvious thing:
>
> u32 val = ~0 << msi->legacy_shift;

Obvious and buggy (from the C standard point of view)? :-)

> Personally I don't think that abusing BIT() in the context of setting
> multiple bits is any better than abusing __GENMASK()...

No, BIT() is not abused here, but __GENMASK().

After all it's up to you, folks, consider that as a bug report.

--
With Best Regards,
Andy Shevchenko