Re: [PATCH] powerpc: Remove eieio in _memcpy_fromio

[Christophe Leroy]

Le 28/01/2025 à 16:24, Christophe Leroy a écrit :
> Le 28/01/2025 à 16:07, Julian Vetter a écrit :
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> >
> > On 1/28/25 15:16, Christophe Leroy wrote:
> > > Le 28/01/2025 à 14:57, Julian Vetter a écrit :
> > > > Remove the eieio() calls in _memcpy_fromio, to bring its implementation
> > > > closer to the one from lib/iomem_copy.c. These eieio() calls don't seem
> > > > to be necessary, because the _memcpy_toio completely omits them. Also
> > > > the legacy code from ppc was not doing them.
> > >
> > > What do you mean exactly by "legacy code" ?
> > >
> > > As far as I can see they were already there before commit 68a64357d15a
> > > ("[POWERPC] Merge 32 and 64 bits asm-powerpc/io.h"):
> >
> > With 'ppc' I was refering to 'include/asm-ppc/io.h'. But you're right,
> > when going back a bit, in the 'include/asm-powerpc/io.h' there are two
> > cases, one (eeh_memcpy_fromio) which does the the 'eieio', and a second,
> > i.e., 'iSeries_memcpy_fromio' which does a byte-wise copy. But in the
> > ppc code ('include/asm-ppc/io.h') there is a simple memcpy. I was
> > referring to this one. But my description is not very clear. Sorry for 
> > that.
>
> But then is your change still valid ? Isn't there some corner case that 
> still need it ? Is it a valid argument that because memcpy_toio() 
> doesn't need it memcpy_fromio() doesn't need it either ?

I see that _insb(), _insw_ns() and _insl_ns() also have eieio() while 
_outsb(), _outsw_ns() and _outsl_ns() don't. Why not change those as 
well if you think eieio() is not needed ?