Memory type used for ioremap

[Shilimkar, Santosh]

> -----Original Message-----
> From: Pedanekar, Hemant
> Sent: Wednesday, August 11, 2010 8:28 PM
> To: Shilimkar, Santosh; Russell King - ARM Linux
> Cc: linux-arm-kernel at lists.infradead.org
> Subject: RE: Memory type used for ioremap
> 
> Shilimkar, Santosh wrote on Wednesday, August 11, 2010 6:34 PM:
> 
> >> -----Original Message-----
> >> From: Pedanekar, Hemant
> >> Sent: Wednesday, August 11, 2010 6:25 PM
> >> To: Shilimkar, Santosh; Russell King - ARM Linux
> >> Cc: linux-arm-kernel at lists.infradead.org
> >> Subject: RE: Memory type used for ioremap
> >>
> >> Shilimkar, Santosh wrote on Wednesday, August 04, 2010 5:35 PM:
> >>
> >>>> -----Original Message-----
> >>>> From: Pedanekar, Hemant
> >>>> Sent: Wednesday, August 04, 2010 5:31 PM
> >>>> To: Shilimkar, Santosh; Russell King - ARM Linux
> >>>> Cc: linux-arm-kernel at lists.infradead.org
> >>>> Subject: RE: Memory type used for ioremap
> >>>>
> >>>> Shilimkar, Santosh wrote:
> >>>>>> Pedanekar, Hemant wrote:
> >>>>>>> Russell King - ARM Linux wrote:
> >>>>>>>> On Fri, Jul 09, 2010 at 07:32:46PM +0530, Pedanekar,
> >>>>> Hemant wrote:
> >>>>>>>>> Catalin,
> >>>>>>>>
> >>>
> >>>> Santosh,
> >>>>
> >>>> Can you please point me to the patch series you mentioned? I will
> give
> >>>> it a try.
> >>> http://www.spinics.net/lists/arm-kernel/msg93218.html
> >>>
> >>
> >> Thanks for the link. I applied the patches and used writel/readl but no
> >> luck. The MT_DEVICE mappings still result into writes not getting
> through.
> >>
> >>>>
> >>>> Regarding read-back, the writes themselves are not successful as the
> >>>> peripheral has specific requirement for non-posted writes. So reading
> >>>> back after write Always returns old value.
> >>>>
> >>> Are you sure about this behaviour?
> >>
> >> Yes. The writes are not going through with MT_DEVICE mappings as the
> target
> >> peripheral has requirement for non-posted writes.
> >>
> >> Looks like only strongly ordered mapping is resulting into non-posted
> >> writes which works. Is there any specific reason the strongly order
> >> mapping patch is not accepted/applied?
> >
> > Attaching one which is I use for debugging. This is only for OMAP3/4
> Hope
> > this is useful to you.
> >
> > I suggest only the device which has non-posted requirement
> > you convert it to SO
> >
> > Regards,
> > Santosh
> 
> Thanks again... yes the writes work fine with SO.
> 
> Is this patch accepted or under review? I don't see it on omap yet.
> 
Last time this was shot down on the basis that barriers and read backs
should fix most of the ordering issues. I am surprised that correct 
barrier + readbacks, didn't work for you.

Can you explain which device has such a requirement with more details.
Most surprising part is, you are observering that a readback is returning
to the write-buffer contents which looks really weird to me.