Re: [PATCH v2] regmap: kunit: Ensure that changed bytes are actually different

[Guenter Roeck]

On 2/9/24 14:39, Mark Brown wrote:
> On Fri, Feb 09, 2024 at 02:07:38PM -0800, Guenter Roeck wrote:
>
> > This is actually worse than v1 because hw_buf[6] isn't used anywhere.
> > Making sure that the values in the val[] array don't match the values
> > in hw_buf[6..7] doesn't add any value.
>
> Yeah, I realised after reading your earlier mail.  It's passing for me
> somehow.

It is passing because the probability for it to fail is really low.
It only fails reliably with the cheat below.

> > FWIW, I had struggled with the re-use of val[0] for two different tests
> > (on hw_buf[2] and hw_buf[4]) myself. The only solution other than making sure
> > that it neither matches hw_buf[2] nor hw_buf[4] I came up with was to use a
> > separate variable for the accesses to hw_buf[4] (or hw_buf[6] in the old code).
> Indeed, it was fine with the old code due to not caring about having
> different values but we need to generate three values now.
>
> >          get_changed_bytes(&hw_buf[6], &val[0], sizeof(val));
> > +       // Let's cheat.
> > +       // Remember, the above code doesn't look into hw_buf[2..5],
> > +       // so anything might be in there, including the values from
> > +       // the val[] array.
> > +       hw_buf[2] = val[0];
> > +       hw_buf[3] = val[1];
> > +       hw_buf[4] = val[0];
> > +       hw_buf[5] = val[1];
>
> I don't understand how this interacts with the pre-sync check?

That is because the test expects the memory in hw_buf[] and val[] to be
different (because hw_buf[] wasn't updated to the new values). The above
cheat forces hw_buf[2,3] and val[0,1] to be the same, so the pre-sync test
fails. The post-sync test passes because the values are expected to be
the same at that time.

Guenter