[PATCH 6/9] Use proper membar instructions on SPARC

[Michael]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hello,

On Aug 13, 2009, at 2:28 AM, Matt Turner wrote:

> On Thu, Aug 13, 2009 at 1:51 AM, David Miller<davem at davemloft.net>  
> wrote:
>> From: Matt Turner <mattst88 at gmail.com>
>> Date: Thu, 13 Aug 2009 01:45:39 -0400
>>
>>> Cc: David S. Miller <davem at davemloft.net>
>>> Cc: Alan Coopersmith <alan.coopersmith at sun.com>
>>> Signed-off-by: Matt Turner <mattst88 at gmail.com>
>>
>> This breaks 32-bit sparc.
>>
>> It will cause the binaries built to be tagged as needing v8plus or v9
>> instructions.  They therefore won't execute or load on a 32-bit sparc
>> system.
>>
>> That's why I encoded the membars using explicit instruction  
>> constants,
>> rather than using the usual mnemonics.
>
> Surely gcc defines a macro we can check for? Something like __sparcv9
> or __arch64__? What is preferred?

__arch64__ doesn't cut it - a 64bit SPARC isn't guaranteed to run in  
64bit mode. I think gcc defines __sparcv9__ when the target allows v9  
instructions ( and v8plus is more or less v9 running with 32bit  
pointers but otherwise full access to v9 instructions IIRC )

> I wanted to do something like this, but I wasn't sure if (1) we needed
> to worry about 32-bit sparc or

NetBSD/sparc 5.0 ships with Xorg 1.4.2, I have 1.6.something working  
on -current. I'm sure OpenBSD and Linux do the same.

> On another note, are load barriers not needed for in{b,w,l} and
> xf86ReadMmio* functions?

Usually SBus, PCI and UPA accesses on sparc are uncached and strongly  
ordered. I'm not quite sure if that's 100% guaranteed though, and  
there are graphics devices on sparc which are neither - they can put  
barriers in their drivers when needed though. As far as I can tell no  
SBus or UPA driver in Xorg uses any barrier macros. Only xf86-video- 
sunffb uses membar #sync but there's no way you can get any of those  
in a 32bit sparc.

have fun
Michael

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (Darwin)

iQEVAwUBSoO4YMpnzkX8Yg2nAQJr+gf/SewXKKySBhGTcRmGCes+dhHJS1SjjAzr
MEa6p4I35BrX0ZV4aQiSm7aPLoSXKGOV319jsDC/9hbeHpRqpjyezGgKLxPowKyt
bem+EuqWDEkFq0Iy3WEwC4UU1KeYELzorlYO9Tuww0SCusvW2845vqrLEV+nSEHz
F+egUmEGHVscuXV1BCmlsqLmNi6JQtqaEARtXLoO5NXdds6PhB6au4+5WngV2Xj5
VewRa/hVRe6II++tiJBxNB47WkLLbhuFMNMQBiMdhyJvRFC2vR6AwFIwIiDDPilu
/hh5G5H0zx36Uup9pyvS3FeTuTrlsFkescTAZfaVS6yX6EIR6DrMiA==
=UHH4
-----END PGP SIGNATURE-----