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

Andy Shevchenko
2021-11-15T14:40:55Z

On Mon, Nov 15, 2021 at 04:14:21PM +0200, Andy Shevchenko wrote:
> 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)? :-)

Forgot to mention that BIT() is also makes it easy to avoid such mistake.

> > 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