On Wed, Jan 16, 2013 at 9:22 AM, Gilles Chanteperdrix <
gilles.chanteperd...@xenomai.org> wrote:
> On 01/16/2013 08:37 AM, Wolfgang Grandegger wrote:
>
> > On 01/15/2013 08:46 PM, Gilles Chanteperdrix wrote:
> >> On 01/15/2013 04:22 PM, Wolfgang Grandegger wrote:
> >>
> >>> From: Wolfgang Grandegger <w...@denx.de>
> >>>
> >>> Pages mapped by rtdm_iomap_to_user() might be cached and may
> >>> page fault on the first write. At least that's the behaviour
> >>> we observed on an ARM mx6q system. This patch fixes these
> >>> issues.
> >>>
> >>> Signed-off-by: Wolfgang Grandegger <w...@denx.de>
> >>> ---
> >>> include/asm-generic/wrappers.h | 2 +-
> >>> ksrc/skins/rtdm/drvlib.c | 8 +++++---
> >>> 2 files changed, 6 insertions(+), 4 deletions(-)
> >>>
> >>> diff --git a/include/asm-generic/wrappers.h
> b/include/asm-generic/wrappers.h
> >>> index de1f0d7..e71bcc3 100644
> >>> --- a/include/asm-generic/wrappers.h
> >>> +++ b/include/asm-generic/wrappers.h
> >>> @@ -394,7 +394,7 @@ static inline void *kzalloc(size_t size, int flags)
> >>> #define wrap_remap_io_page_range(vma,from,to,size,prot) ({
> \
> >>> (vma)->vm_page_prot = pgprot_noncached((vma)->vm_page_prot); \
> >
> > Hm, here pgprot_noncached() is already used.
> >
> >>> /* Sets VM_RESERVED | VM_IO | VM_PFNMAP on the vma. */ \
> >>> - remap_pfn_range(vma,from,(to) >> PAGE_SHIFT,size,prot);
> \
> >>> + remap_pfn_range(vma,from,(to) >>
> PAGE_SHIFT,size,pgprot_noncached(prot)); \
> >>
> >>
> >> Should not this be decided in the upper layers?
> >
> > Upper layers? You mean calling xnarch_remap_io_page_range() with the
> > protection argument "pgprot_noncached(PAGE_SHARED)" in
> rtdm_mmap_buffer()?
>
>
> I mean users could want to map i/o regions cacheable, but as you say,
> the pgprot_noncached is already hardcoded in the vma, so, I will merge
> your patch.
>
I used rtdm_iomap_to_user() to map the iMX6 EIM device into user space and
still see caching behavior.
Wolfgang, your patch didn't apply the pgprot_noncached(prot) to the #if
LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,15) && defined(CONFIG_MMU) case.
Was that intended? Were you using a non-mmu configuration or an old kernel?
Anyway, when I apply that change to the >v2.6.15&mmu case, then the caching
behavior is gone. I think that is correct, because my assumption is the
>v2.6.15&mmu check should only switch the use of vm_insert_page(). Please
comment on this assumption.
If the assumption is correct, then select one of the attached patches. The
first one just adds the pgprot_noncached(prot) to the >v2.6.15&mmu case,
while version 2 removes removes the duplicate code
for wrap_remap_io_page_range() and wrap_remap_kmem_page_range(). So NOTE to
only select one of the patches.
Thanks,
Henri
>
> --
> Gilles.
>
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