Re: [PATCH 1/1] mfd: tps65911-comparator: Fix an off by one bug

From: Lee Jones
Date: Tue May 01 2018 - 09:22:20 EST


On Tue, 01 May 2018, Robin Murphy wrote:

> On 01/05/18 10:45, Lee Jones wrote:
> > The COMP1 and COMP2 elements are in 0 and 1 respectively so this code is
> > accessing the wrong elements and one space beyond the end of the array.
> >
> > The "id" variable is never COMP (0) so that code can be removed.
> >
> > Fixes: 6851ad3ab346 ("TPS65911: Comparator: Add comparator driver")
> > Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > ---
> >
> > History:
> >
> > Dan was the originator of this patch and the author of the commit log,
> > but produced 2 code solutions which I wasn't happy with. The first
> > submission [0] introduced a COMP device, which after a quick check of
> > the datasheet [1] appeared to be fictitious. A subsequent submission
> > [2] conducted arithmetic in array indexes.
> >
> > It is my belief that the correct solution is to roll which the
> > situation the hardware engineers presented us with and define COMP1
> > at position 0 and COMP2 at position 1 such that we can use the
> > simplest code possible to select them.
> >
> > Dan wasn't happy to put his name to this, which I completely
> > understand. Calling SOMETHING1 0 (zero) is a little unnatural.
> >
> > However, since I have no shame, I offered to submit it.
>
> As an idly-curious passer-by, this looks perfectly reasonable to me - I
> don't see why a mapping between names and indices should have to be
> artificially constrained just because the names happen to contain numerals.

Right. This was my thinking too.

> If it's really that abhorrent, then I guess they could be named something
> like COMPn_ID for even more clarity.
>
> That said, now that I've gone and looked, the whole business seems
> ridiculously over-engineered. AFAICS it would be infinitely simpler to just
> pass the register address directly where id is currently passed, statically
> define UV_MAX, and get rid of the otherwise-pointless struct comparator
> entirely. The current abstraction doesn't look like it could actually scale
> to support different chips without major surgery anyway.

Sounds good. Patches always welcome. ;)

--
Lee Jones [æçæ]
Linaro Services Technical Lead
Linaro.org â Open source software for ARM SoCs
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