Re: [PATCH v4 4/8] rt2800: fix registers init for MT7620

[Stanislaw Gruszka]

On Fri, Oct 12, 2018 at 02:41:41PM +0200, Tom Psyborg wrote:
> On 12/10/2018, Stanislaw Gruszka <sgrus...@redhat.com> wrote:
> > On Fri, Oct 12, 2018 at 02:20:07PM +0200, Tom Psyborg wrote:
> >> > On upstream tree where this patch is intended
> >> > additional registers where never programmed as proper branch
> >> > were never used, because of additional check in RT5390 branch.
> >> >
> >>
> >> on my hardware additional registers were programmed in regardless of
> >> redundant check. that why i opened whole thread on forum since i
> >> couldn't understand how's that happening
> >
> > I don't understand how that possible either.
> 
> i'd assume because device use external lna

I have no idea how this could be related. But I think I found
somewhat reasonable explenation where the problem is.
I think below code :

        if (a || b || c) {
                CODE1();
        } else if (c) {
                CODE2();
        }

can not be deterministic and can be compiled differently depending
on compiler version and used options. Sometimes it could result
in this 

        if (a || b || c) {
                CODE1();
        }

and sometimes in this:

        if (a || b) {
                CODE1();
        } else if (c) {
                CODE2();
        }

So that would explain the problems you see. And indeed patch
could cause regression on systems where second variant of
initalizing RT6352 registers was used.

Thanks
Stanislaw