Hi,
El Fri, May 05, 2017 at 01:29:32PM -0700 Grant Grundler ha dit:
> On Fri, May 5, 2017 at 1:08 PM, Ville Syrjälä
> <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> ...
> >> > I'm not convinced the patch is making things any better really. To
> >> > fix this really properly, I think we'd need to introduce a new enum
> >> > pch_transcoder and thus avoid the confusion of which type of
> >> > transcoder we're talking about.
I agree, the patch certainly doesn't improve the confusing use of the enums.
> >> Is an enum better than coding an explicit conversion in an inline function?
> >
> > The point of the enum would be to make it more clear which piece of
> > hardware we're talking to in each case.
>
> Ah ok - I misunderstood - I thought this was already the case.
>
> > But this would require going
> > through the entire PCH code and changing things to use the right type
> > in each case. Quite a bit of work with little measurable gain I'd say.
>
> IMHO, one of the best things that happened to C standard was addition
> of strong type checking. It's helped prevent developers from making
> one class of "stupid mistakes". So while this change wouldn't improve
> performance, it would allow a form of automated correctness checking
> that can be enforced with every patch you get (every time the code
> base is compiled).
>
> In other words, the gain isn't currently measurable the same way
> performance is but I believe it's worth doing. Given the number of
> typedefs and enums in kernel code, I suspect most kernel developers
> would agree.
I also think that proper use of enums is an additional line of defense
against "stupid mistakes". While weeding out these warnings in
different drivers I came across a few cases were the code was working
out of sheer luck because the (unintentionally) mismatched enums
resolved to the same value.
Cheers
Matthias
> >> Then the code can do some sanity checking as well. Something like:
> >>
> >> enum transcoder pch_to_cpu_enum(enum pipe)
> >> {
> >> WARN_ON(pipe > FOO);
> >> return (enum transcoder) pipe;
> >> }
> >
> > That would have to be called pipe_to_pch_transcoder() or something like
> > that.
> >
> >>
> >> > Currently most places expect an
> >> > enum pipe when dealing with PCH transcoders, and enum transcoder
> >> > when dealing with CPU transcoders. But there are some exceptions
> >> > of course.
> >>
> >> cheers,
> >> grant
> >> >
> >
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