linux-kernel - Re: [PATCH] x86: Remove 32-bit versions of readq()/writeq()

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Date:	Fri, 20 May 2011 16:03:09 +0400
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Roland Dreier <roland@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Milton Miller <miltonm@....com>,
	Hitoshi Mitake <h.mitake@...il.com>,
	Kashyap Desai <Kashyap.Desai@....com>,
	Len Brown <lenb@...nel.org>,
	Ravi Anand <ravi.anand@...gic.com>,
	Vikas Chaudhary <vikas.chaudhary@...gic.com>,
	Matthew Garrett <mjg@...hat.com>
Subject: Re: [PATCH] x86: Remove 32-bit versions of readq()/writeq()

On Fri, 2011-05-20 at 13:44 +0200, Ingo Molnar wrote:
> * Roland Dreier <roland@...nel.org> wrote:
> 
> > From: Roland Dreier <roland@...estorage.com>
> > 
> > The presense of a writeq() implementation on 32-bit x86 that splits
> > the 64-bit write into two 32-bit writes turns out to break the mpt2sas
> > driver (and in general is risky for drivers as was discussed in
> > <http://lkml.kernel.org/r/adaab6c1h7c.fsf@cisco.com>).  To fix this,
> > revert 2c5643b1c5c7 ("x86: provide readq()/writeq() on 32-bit too")
> > and follow-on cleanups.
> > 
> > This unfortunately leads to pushing non-atomic definitions of readq()
> > and write() to various x86-only drivers that in the mean time started
> > using the definitions in the x86 version of <asm/io.h>.  However as
> > discussed exhaustively, this is actually the right thing to do,
> > because the right way to split a 64-bit transaction is hardware
> > dependent and therefore belongs in the hardware driver (eg mpt2sas
> > needs a spinlock to make sure no other accesses occur in between the
> > two halves of the access).
> > 
> > Build tested on 32- and 64-bit x86 allmodconfig.
> > 
> > Link: http://lkml.kernel.org/r/x86-32-writeq-is-broken@mdm.bga.com
> > Cc: Hitoshi Mitake <h.mitake@...il.com>
> > Cc: Kashyap Desai <Kashyap.Desai@....com>
> > Cc: Len Brown <lenb@...nel.org>
> > Cc: Ravi Anand <ravi.anand@...gic.com>
> > Cc: Vikas Chaudhary <vikas.chaudhary@...gic.com>
> > Cc: Matthew Garrett <mjg@...hat.com>
> > Signed-off-by: Roland Dreier <roland@...estorage.com>
> > ---
> >  arch/x86/Kconfig                 |    2 --
> >  arch/x86/include/asm/io.h        |   24 ++----------------------
> >  drivers/acpi/apei/einj.c         |    8 ++++++++
> >  drivers/acpi/atomicio.c          |    4 ++++
> >  drivers/edac/i3200_edac.c        |   13 +++++++++++++
> >  drivers/platform/x86/ibm_rtl.c   |   13 +++++++++++++
> >  drivers/platform/x86/intel_ips.c |   13 +++++++++++++
> >  drivers/scsi/qla4xxx/ql4_nx.c    |   21 +++++++++++++++++++++
> >  8 files changed, 74 insertions(+), 24 deletions(-)
> 
> Hm, this patch is wider than i thought - might be better to do this via one of 
> the driver trees or -mm?

We don't have a single driver tree covering all of those, so I think the
x86 tree is as good as any other

> The x86 bits are:
> 
> Acked-by: Ingo Molnar <mingo@...e.hu>

For the SCSI bits:

Acked-by: James Bottomley <James.Bottomley@...allels.com>

James


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