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SubjectRe: [PATCH] libata-sff: fix 32-bit PIO regression
Sergei Shtylyov writes:
> Hello.
>
> Hugh Dickins wrote:
>
> >> Commit 871af1210f13966ab911ed2166e4ab2ce775b99d (libata: Add 32bit PIO support)
> >> caused all kind of errors on the ATAPI devices, so it's been empirically proven
> >> that one shouldn't read/write an extra data word when a device isn't expecting
> >> it already. "Don't do it then"; however still taking a chance to use 32-bit I/O
> >> one last time when there are exactly 3 trailing bytes. Oh, and stop pointless
> >> swapping bytes to and fro as well by using io*_rep() which shouldn't byte-swap.
> >>
> >> This should fix the kernel.org bug #12609.
> >>
> >> ---
> >> This is hopefully better replacement for Hugh Dickins most recent patch
> >> (http://marc.info/?l=linux-ide&m=123352294619281)...
> >>
> >
> > Yes, looks nice, and works for me. My only criticism would be,
> > minor issue unchanged by your patch, that actually "slop" isn't
> > unlikely enough to deserve an "unlikely" - slop of 1 or 3 is
> > unlikely, but slop of 2 is quite common.
> >
>
> I guess that's the case only for the ATAPI devices, so I'm going to
> keep it.

I really don't think it's a good idea to play micro-optimisation
unlikely() tricks when the likelihood depends on what kind of device
the driver is talking to. In this case unlikely() is clearly wrong.


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