Subject: Re: [PATCH] powerpc: Implement dma_mmap_coherent()

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 29 Mar 2011 11:30:06 +1100

On Fri, 2011-03-25 at 17:50 +1100, Benjamin Herrenschmidt wrote:
> This is used by Alsa to mmap buffers allocated with dma_alloc_coherent()
> into userspace. We need a special variant to handle machines with
> non-coherent DMAs as those buffers have "special" virt addresses and
> require non-cachable mappings

Missing an EXPORT_SYMBOL_GPL... will fix that up before I merge.

Cheers,
Ben.

> Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
> ---
> 
> Dunno if anybody with CONFIG_NOT_COHERENT_CACHE has some audio device
> that uses dma buffers (ie not usb-audio) and wants to try that out...
> should fix a long standing problem.
> 
>  arch/powerpc/include/asm/dma-mapping.h |    7 +++++++
>  arch/powerpc/kernel/dma.c              |   18 ++++++++++++++++++
>  arch/powerpc/mm/dma-noncoherent.c      |   20 ++++++++++++++++++++
>  3 files changed, 45 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h
> index 6d2416a..41e0eb7 100644
> --- a/arch/powerpc/include/asm/dma-mapping.h
> +++ b/arch/powerpc/include/asm/dma-mapping.h
> @@ -42,6 +42,7 @@ extern void __dma_free_coherent(size_t size, void *vaddr);
>  extern void __dma_sync(void *vaddr, size_t size, int direction);
>  extern void __dma_sync_page(struct page *page, unsigned long offset,
>  				 size_t size, int direction);
> +extern unsigned long __dma_get_coherent_pfn(void *cpu_addr);
>  
>  #else /* ! CONFIG_NOT_COHERENT_CACHE */
>  /*
> @@ -52,6 +53,7 @@ extern void __dma_sync_page(struct page *page, unsigned long offset,
>  #define __dma_free_coherent(size, addr)		((void)0)
>  #define __dma_sync(addr, size, rw)		((void)0)
>  #define __dma_sync_page(pg, off, sz, rw)	((void)0)
> +#define __dma_get_coherent_pfn(cpu_addr)	(0)
>  
>  #endif /* ! CONFIG_NOT_COHERENT_CACHE */
>  
> @@ -198,6 +200,11 @@ static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr)
>  #define dma_alloc_noncoherent(d, s, h, f) dma_alloc_coherent(d, s, h, f)
>  #define dma_free_noncoherent(d, s, v, h) dma_free_coherent(d, s, v, h)
>  
> +extern int dma_mmap_coherent(struct device *, struct vm_area_struct *,
> +			     void *, dma_addr_t, size_t);
> +#define ARCH_HAS_DMA_MMAP_COHERENT
> +
> +
>  static inline void dma_cache_sync(struct device *dev, void *vaddr, size_t size,
>  		enum dma_data_direction direction)
>  {
> diff --git a/arch/powerpc/kernel/dma.c b/arch/powerpc/kernel/dma.c
> index cf02cad..0f52235 100644
> --- a/arch/powerpc/kernel/dma.c
> +++ b/arch/powerpc/kernel/dma.c
> @@ -179,3 +179,21 @@ static int __init dma_init(void)
>         return 0;
>  }
>  fs_initcall(dma_init);
> +
> +int dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma,
> +		      void *cpu_addr, dma_addr_t handle, size_t size)
> +{
> +	unsigned long pfn;
> +
> +#ifdef CONFIG_NOT_COHERENT_CACHE
> +	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> +	pfn = __dma_get_coherent_pfn(cpu_addr);
> +#else
> +	pfn = page_to_pfn(virt_to_page(cpu_addr));
> +#endif
> +	return remap_pfn_range(vma, vma->vm_start,
> +			       pfn + vma->vm_pgoff,
> +			       vma->vm_end - vma->vm_start,
> +			       vma->vm_page_prot);
> +}
> +
> diff --git a/arch/powerpc/mm/dma-noncoherent.c b/arch/powerpc/mm/dma-noncoherent.c
> index 757c0be..174b10a 100644
> --- a/arch/powerpc/mm/dma-noncoherent.c
> +++ b/arch/powerpc/mm/dma-noncoherent.c
> @@ -399,3 +399,23 @@ void __dma_sync_page(struct page *page, unsigned long offset,
>  #endif
>  }
>  EXPORT_SYMBOL(__dma_sync_page);
> +
> +/*
> + * Return the PFN for a given cpu virtual address returned by
> + * __dma_alloc_coherent. This is used by dma_mmap_coherent()
> + */
> +unsigned long __dma_get_coherent_pfn(void *cpu_addr)
> +{	
> +	/* This should always be populated, so we don't test every
> +	 * level. If that fails, we'll have a nice crash which
> +	 * will be as good as a BUG_ON()
> +	 */
> +	pgd_t *pgd = pgd_offset_k(cpu_addr);
> +	pud_t *pud = pud_offset(pgd, cpu_addr);
> +	pmd_t *pmd = pmd_offset(pud, cpu_addr);
> +	pte_t *ptep = pte_offset_kernel(pmd, cpu_addr);
> +
> +	if (pte_none(*ptep) || !pte_present(*ptep))
> +		return 0;
> +	return pte_pfn(*ptep);	
> +}
> 
> 
> 
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