Re: [Linux-fbdev-devel] [PATCH] video: arch specific page protection support for deferred io

[Paul M. <le...@li...>]

On Fri, Jun 26, 2009 at 02:36:23AM +0800, Jaya Kumar wrote:
> On Fri, Jun 26, 2009 at 2:12 AM, Andrew Morton<ak...@li...> wrote:
> > On Fri, 26 Jun 2009 02:38:06 +0900
> > Paul Mundt <le...@li...> wrote:
> >
> >> On Thu, Jun 25, 2009 at 12:03:59AM -0700, Andrew Morton wrote:
> >> > On Thu, 25 Jun 2009 15:06:24 +0900 Magnus Damm <mag...@gm...> wrote:
> >> > > There are 3 levels of dependencies:
> >> > > 1: pgprot_noncached() patches from Arnd
> >> > > 2: mm: uncached vma support with writenotify
> >> > > 3: video: arch specfic page protection support for deferred io
> >> > >
> >> > > 2 depends on 1 to compile, but 3 (this one) is disconnected from 2 and
> >> > > 1. So this patch can be merged independently.
> > <hunts around and finds #2>
> >
> > I don't really understand that one. ?Have we heard fro Jaya recently?
> >
> 
> He's been having some personal problems so he's been quiet. :-)
> 
> Magnus's defio changes, #3 look fine to me. I don't know much about #2
> but what I understood was that the previous mmap_region code was
> unintentionally turning caching back on when it did the writenotify
> test and I guess Magnus's goal with the patch is to make sure that
> address range is left uncached since sh_mobile uses DMA to transfer
> the framebuffer and he might have encountered coherency issues there?
> 
Correct. This could have been documented a bit better, but yes, the issue
is that when the writenotify test kicks in the vma silently loses its
uncachedness which leads to the aforementioned runtime behaviour issues.