Re: [Xen-devel] [RFC 02/14] xen/arm: Remove the parameter "attrindx" in copy_paddr

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-03-17 at 11:53 +0000, Julien Grall wrote:
> Hi Ian,
> 
> On 03/17/2014 10:13 AM, Ian Campbell wrote:
> > On Fri, 2014-03-14 at 18:02 +0000, Julien Grall wrote:
> >> Hi Ian,
> >>
> >> On 03/14/2014 05:14 PM, Ian Campbell wrote:
> >>> On Wed, 2014-03-12 at 16:15 +0000, Julien Grall wrote:
> >>>> copy_addr
> >>>
> >>> s/copy_p?addr/copy_from_paddr/ throughout the subject and changelog.
> >>
> >> Right. I will fix it in the next series.
> >>
> >>>>  is only used with BUFFERABLE, there is some place where DEV_SHARED
> >>>> was used by mistake.
> >>>
> >>> A hangover from flash support or something else?
> >>
> >> I guess, DEV_SHARED was using in few place mainly when Xen is loading a
> >> small amount of data. Even before this patch, info->load_attr should
> >> have been used.
> >>
> >> Do you think I need to send a patch for Xen 4.4?
> > 
> > Is it actively harmful or just not ideal?
> 
> From the ARM ARM A3.5.1, we should use Normal memory attribute even for
> the flash.

For r/o access that does make sense. I expect when programming or
sending control commands more cleverness is needed, but we needn't worry
here. Good.

> I'm not sure what is the behavior when Normal memory is access with
> Device memory attribute.

It's just pointlessly uncached and strongly ordered I think, so it's a
performance hit.

Ian.


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