Re: [PATCH v3 0/6] RTL8231 GPIO expander support

Linus Walleij
2021-06-01T11:48:59Z

On Tue, Jun 1, 2021 at 1:41 PM Michael Walle <michael@walle.cc> wrote:
> Am 2021-06-01 12:51, schrieb Linus Walleij:
> > On Tue, Jun 1, 2021 at 12:18 PM Michael Walle <michael@walle.cc> wrote:
> >> Am 2021-06-01 11:59, schrieb Linus Walleij:
> >
> >> > Just regarding all registers/memory cells in a register page
> >> > as default volatile (which is what we do a lot of the time)
> >> > has its upsides: bugs like this doesn't happen.
> >>
> >> I don't think this is the bug here. If it is really a write-only
> >> register
> >> the problem is the read in RMW. Because reading the register will
> >> return
> >> the input value instead of the (previously written) output value.
> >
> > True that. Write and read semantics differ on the register.
> >
> > Volatile is used for this and some other things,
> > like for example interrupts being cleared when a register
> > is read so it is strictly read-once.
>
> Isn't that what precious is for?

I never figured that one out. But I assume you are right.

Proper regmap semantics documentation is forthcoming! ;)

Yours,
Linus Walleij