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

From: James Bottomley
Date: Fri May 20 2011 - 08:07:14 EST


On Fri, 2011-05-20 at 13:44 +0200, Ingo Molnar wrote:
> * Roland Dreier <roland@xxxxxxxxxx> wrote:
>
> > From: Roland Dreier <roland@xxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxx>). 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@xxxxxxxxxxx
> > Cc: Hitoshi Mitake <h.mitake@xxxxxxxxx>
> > Cc: Kashyap Desai <Kashyap.Desai@xxxxxxx>
> > Cc: Len Brown <lenb@xxxxxxxxxx>
> > Cc: Ravi Anand <ravi.anand@xxxxxxxxxx>
> > Cc: Vikas Chaudhary <vikas.chaudhary@xxxxxxxxxx>
> > Cc: Matthew Garrett <mjg@xxxxxxxxxx>
> > Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
> > ---
> > 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@xxxxxxx>

For the SCSI bits:

Acked-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxx>

James


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