* What is the reel purpose of in_beXX() and out_beXX() fonctions ?
@ 2014-10-27 12:52 leroy christophe
2014-10-27 15:05 ` David Laight
2014-10-27 16:45 ` Scott Wood
0 siblings, 2 replies; 4+ messages in thread
From: leroy christophe @ 2014-10-27 12:52 UTC (permalink / raw)
To: LinuxPPC-dev, Scott Wood, Benjamin Herrenschmidt
Many drivers use in_be16(), in_be32(), out_be16(), out_be32(), etc ....
to access to registrers in IO mapped memory.
What is the real purpose of those functions, and are they really needed ?
ioremap() maps the related areas as GUARDED, which means that accesses
can't be speculative. So what is the benefit of using in_beXX() and
out_beXX() over simple memory accesses in the area ?
Christophe
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: What is the reel purpose of in_beXX() and out_beXX() fonctions ?
2014-10-27 12:52 What is the reel purpose of in_beXX() and out_beXX() fonctions ? leroy christophe
@ 2014-10-27 15:05 ` David Laight
2014-10-27 21:11 ` Benjamin Herrenschmidt
2014-10-27 16:45 ` Scott Wood
1 sibling, 1 reply; 4+ messages in thread
From: David Laight @ 2014-10-27 15:05 UTC (permalink / raw)
To: 'leroy christophe',
LinuxPPC-dev, Scott Wood, Benjamin Herrenschmidt
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: What is the reel purpose of in_beXX() and out_beXX() fonctions ?
2014-10-27 12:52 What is the reel purpose of in_beXX() and out_beXX() fonctions ? leroy christophe
2014-10-27 15:05 ` David Laight
@ 2014-10-27 16:45 ` Scott Wood
1 sibling, 0 replies; 4+ messages in thread
From: Scott Wood @ 2014-10-27 16:45 UTC (permalink / raw)
To: leroy christophe; +Cc: LinuxPPC-dev
On Mon, 2014-10-27 at 13:52 +0100, leroy christophe wrote:
> Many drivers use in_be16(), in_be32(), out_be16(), out_be32(), etc ....
> to access to registrers in IO mapped memory.
>
> What is the real purpose of those functions, and are they really needed ?
>
> ioremap() maps the related areas as GUARDED, which means that accesses
> can't be speculative. So what is the benefit of using in_beXX() and
> out_beXX() over simple memory accesses in the area ?
Speculative accesses aren't the only issue -- there's also hardware
reordering (some implementations may not do this on guarded regions, but
I don't think it's architecturally guaranteed), and of course you need
to make sure the compiler doesn't do anything funny.
-Scott
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: What is the reel purpose of in_beXX() and out_beXX() fonctions ?
2014-10-27 15:05 ` David Laight
@ 2014-10-27 21:11 ` Benjamin Herrenschmidt
0 siblings, 0 replies; 4+ messages in thread
From: Benjamin Herrenschmidt @ 2014-10-27 21:11 UTC (permalink / raw)
To: David Laight; +Cc: Scott Wood, LinuxPPC-dev
On Mon, 2014-10-27 at 15:05 +0000, David Laight wrote:
>
> Unfortunately the functions sometimes contain additional (often
> unneeded)
> sequencing instructions - the driver may be able to perform multiple
> operations between the sequencing instructions.
That's in part why some folks are working on proper relaxed accessors
(see Will Deacon's stuff)
Cheers,
Ben.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2014-10-27 21:17 UTC | newest]
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2014-10-27 12:52 What is the reel purpose of in_beXX() and out_beXX() fonctions ? leroy christophe
2014-10-27 15:05 ` David Laight
2014-10-27 21:11 ` Benjamin Herrenschmidt
2014-10-27 16:45 ` Scott Wood
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