Re: PowerPC equivalent to dma_mmap_writecombine()?

Re: PowerPC equivalent to dma_mmap_writecombine()?

[Arnd Bergmann]

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PowerPC equivalent to dma_mmap_writecombine()?

[Timur Tabi]

I'm porting a driver from ARM to PowerPC, and I came across this function:

static int at91_pcm_mmap(struct snd_pcm_substream *substream,
	struct vm_area_struct *vma)
{
	struct snd_pcm_runtime *runtime = substream->runtime;

	return dma_mmap_writecombine(substream->pcm->card->dev, vma,
				     runtime->dma_area,
				     runtime->dma_addr,
				     runtime->dma_bytes);
}

There are no dma_mmap_x() functions in arch/powerpc.  Can someone tell me what the powerpc 
equivalent to dma_mmap_writecombine() is?

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

Re: PowerPC equivalent to dma_mmap_writecombine()?

[Segher Boessenkool]

>> There are no dma_mmap_x() functions in arch/powerpc.  Can someone  
>> tell me what the powerpc
>> equivalent to dma_mmap_writecombine() is?
>
> 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.

Either that, or just map it as normal cache-coherent DMA
memory.


Segher

Re: PowerPC equivalent to dma_mmap_writecombine()?

[Timur Tabi]

Arnd Bergmann wrote:

> 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.

I always have a hard time with these mapping functions.  Is this right?

vma->vm_page_prot = __pgprot((pgprot_val(vma->vm_page_prot) | _PAGE_NO_CACHE) & 
~_PAGE_GUARDED));

ret = remap_pfn_range(vma, vma->vm_start, runtime->dma_addr, runtime->dma_bytes, 
vma->vm_page_prot);

Alternatively, could I use function snd_pcm_lib_mmap_iomem() (sound/core/pcm_native.c)? 
It looks like it does the right thing, although it doesn't unset the guarded bit.  If 
that's wrong, I can submit a patch to unset that bit on PowerPC, but like I said, I can 
never quite get my head around this mapping stuff.

-- 
Timur Tabi
Linux Kernel Developer @ Freescale

Re: PowerPC equivalent to dma_mmap_writecombine()?

[Arnd Bergmann]

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 <><