Re: [PATCH v2 2/4] serial: 8250_dw: Only accept a contiguous DLF readback

[Ilpo Järvinen]

On Tue, 20 Oct 2026, Andy Shevchenko wrote:

> On Tue, Oct 20, 2026 at 08:11:06AM +0200, Jiri Slaby wrote:
> > On 19. 10. 26, 22:06, Vinicius Pedrosa wrote:
> 
> ...
> 
> > > -	if (reg) {
> > > +	/*
> > > +	 * DLF is a bit field starting at bit 0, so a real one reads back as
> > > +	 * 2^n - 1. Any other value means this offset is something else.
> > > +	 */
> > > +	if (reg && !(reg & (reg + 1))) {
> > 
> > Do I understand correctly, that this equivalent to:
> >   if (is_power_of_2(reg + 1))
> > ?
> 
> Yes, and since we check for reg to be "not zero", this will work the rest.

For is_power_of_2(), 0 is not a power of two. And it also wouldn't make 
sense to have zero bits in the bit field as it's same as no bit field so 
using just is_power_of_2() should be enough.

It could be that's what Andy meant, but the wording left too much room 
for interpretation.

-- 
 i.