Re: Problem with remap_page_range

[Matt Porter <mporter@kernel.crashing.org>]

On Tue, Sep 09, 2003 at 09:13:49PM -0400, Dmytro Bablinyuk wrote:
> 
> We have a DSP shared memory which we should access (from PowerPC).
> The problem is when I do ioremap I can see the memory correctly from the 
> driver (see below) but when I do remap_page_range to the user space 
> application then data appears to be wrong, I can recognize some values 
> there, but they are in the wrong places and other values around from 
> everywhere else (see below).

<snip>

>   if (remap_page_range(vma->vm_start,
>                        DSP_ADDR,
>                        size,
>                        vma->vm_page_prot
>                        ))

Your remap call isn't adding _PAGE_NO_CACHE and _PAGE_GUARDED flags
like ioremap_nocache()/ioremap() do on PPC.  You'll get bad results
because of the ordering and cache issues resulting from not using
these PTE flags.  In 2.6, these can be added using pgprot_noncached()
that is defined per-arch.

BTW, ioremap_nocache() and ioremap() are identical on PPC.

-Matt