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From: Arnd Bergmann <arnd@arndb.de>
To: Timur Tabi <timur@freescale.com>
Subject: Re: PowerPC equivalent to dma_mmap_writecombine()?
Date: Fri, 6 Jul 2007 23:26:22 +0200
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On Friday 06 July 2007, Timur Tabi wrote:
> Arnd Bergmann wrote:
>=20
> > Not sure exactly what arm does here, but it sounds like you want
> > to call remap_pfn_range with the _PAGE_NO_CACHE bit set in the
> > protection flags, and _PAGE_GUARDED not set.
>=20
> I always have a hard time with these mapping functions. =A0Is this right?
>=20
> vma->vm_page_prot =3D __pgprot((pgprot_val(vma->vm_page_prot) | _PAGE_NO_=
CACHE) &=20
> ~_PAGE_GUARDED));
>=20
> ret =3D remap_pfn_range(vma, vma->vm_start, runtime->dma_addr, runtime->d=
ma_bytes,=20
> vma->vm_page_prot);
>=20
> Alternatively, could I use function snd_pcm_lib_mmap_iomem() (sound/core/=
pcm_native.c)?=20
> It looks like it does the right thing, although it doesn't unset the guar=
ded bit. =A0If=20
> that's wrong, I can submit a patch to unset that bit on PowerPC, but like=
 I said, I can=20
> never quite get my head around this mapping stuff.

The guarded bit is disabled by default, so you don't need t remove it, so
the function you quoted should be alright for this purpose. Not sure if you
need the ioremap in there though.

	Arnd <><