[Toybox] [PATCH] devmem: Fix 8 byte wide writes

[enh]

On Fri, Oct 6, 2023 at 12:35 PM Michael Shavit via Toybox
<toybox at lists.landley.net> wrote:
>
> On Fri, Oct 6, 2023 at 4:41 AM Rob Landley <rob at landley.net> wrote:
> >
> > I could adjust _just_ addr to use unsigned long instead of unsigned long long,
> > but I don't want two atollu()/atolu() and letting you do a longer address and
> > silently truncating it isn't great either. Also, a 32-bit platform can't do an
> > atomic 64 bit read/write either (it's gonna do 2 32 bit ones behind the scenes)
> > and I kinda don't want to claim it won't? Which means removing the 8 byte option
> > when building for 32 bits, which is trivial to do in the code:
> >
> > +    else if (sizeof(long)==8 && bytes==8) *(unsigned long *)p = data;
>
>
> We can also emit an error earlier in the function if the WIDTH
> parameter is 8 on a 32 bit platform.
>
> IMO disallowing 64bit writes is less risky of headaches than silently
> non-atomic behavior.  A clear error message might help alleviate the
> documentation issue, but I'll agree it's less than ideal to find out
> that something won't work after the fact.

eh, i actually _prefer_ the error message option --- if someone tries
this on a 32-bit device, they're probably confused enough that an
error message will be helpful. whereas seeing nothing in the --help
text is unlikely to teach them anything.

(bruce tognazzini used to argue against graying out menu items/buttons
in guis for similar reasons --- "how can you teach the user what
they've done wrong in that case?". i've never been annoyed by an
explanation of what i'm doing wrong, but i've often been annoyed by a
button i can't click and don't understand why!)

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