Re: [RFC PATCH 2/2] treewide, bits: use ffs_val() where it is open-coded

[Maciej W. Rozycki]

On Sat, 10 Jan 2026, David Laight wrote:

> > > > diff --git a/arch/mips/dec/ecc-berr.c b/arch/mips/dec/ecc-berr.c
> > > > index 1eb356fdd8323..8934b8b1cf375 100644
> > > > --- a/arch/mips/dec/ecc-berr.c
> > > > +++ b/arch/mips/dec/ecc-berr.c
> > > > @@ -153,7 +153,7 @@ static int dec_ecc_be_backend(struct pt_regs *regs, int is_fixup, int invoker)
> > > >  			/* Ack now, now we've rewritten (or not). */
> > > >  			dec_ecc_be_ack();
> > > >  
> > > > -			if (syn && syn == (syn & -syn)) {
> > > > +			if (syn && syn == ffs_val(syn)) {  
> > > 
> > > It opencodes is_power_of_2().
> 
> Badly...

 It's 4 MIPS instructions and exactly the same machine code produced as 
compiler output from `is_power_of_2'.  If you know of a better alternative 
I'll be happy to get enlightened, however it's academic anyway, as it's 
the ECC memory error handler.  If you get here, then you have a bigger 
issue than a couple of extra instructions executed per kernel log entry 
produced.  If you indeed can get rid of them in the first place, that is.

  Maciej