Re: [Linaro-mm-sig] [PATCH][RFC] arm: dma-mapping: Add support for allocating/mapping cached buffers

[Laura Abbott <lauraa@xxxxxxxxxxxxxx>]

On 7/14/2012 6:53 AM, Clark, Rob wrote:
> On Fri, Jul 13, 2012 at 1:01 PM, Laura Abbott <lauraa@xxxxxxxxxxxxxx> wrote:
> > There are currently no dma allocation APIs that support cached
> > buffers. For some use cases, caching provides a signficiant
> > performance boost that beats write-combining regions. Add
> > apis to allocate and map a cached DMA region.
>
> btw, there were recent patches for allocating dma memory without a
> virtual mapping.  With this you could map however you want to
> userspace (for example, cached)
>
> I'm assuming that you are not needing it to be mapped cached to kernel?

Thanks for reminding me about those patches. They don't quite solve the 
problem as is for two reasons: 1) I'm looking at regular CMA 
allocations, not iommu allocations which is what the patches covered 2) 
I do actually need a kernel cached mapping in addition to the userspace 
mappings.

I've obviously missed the last DMA rework patches, and I should 
rebase/rework against those. Is another DMA attribute (DMA_ATTR_CACHED) 
an acceptable option?

> BR,
> -R

Thanks,
Laura

> > Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
> > ---
> >   arch/arm/include/asm/dma-mapping.h |   21 +++++++++++++++++++++
> >   arch/arm/mm/dma-mapping.c          |   21 +++++++++++++++++++++
> >   2 files changed, 42 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> > index dc988ff..1565403 100644
> > --- a/arch/arm/include/asm/dma-mapping.h
> > +++ b/arch/arm/include/asm/dma-mapping.h
> > @@ -239,12 +239,33 @@ int dma_mmap_coherent(struct device *, struct vm_area_struct *,
> >   extern void *dma_alloc_writecombine(struct device *, size_t, dma_addr_t *,
> >                  gfp_t);
> >
> > +/**
> > + * dma_alloc_cached - allocate cached memory for DMA
> > + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
> > + * @size: required memory size
> > + * @handle: bus-specific DMA address
> > + *
> > + * Allocate some cached memory for a device for
> > + * performing DMA.  This function allocates pages, and will
> > + * return the CPU-viewed address, and sets @handle to be the
> > + * device-viewed address.
> > + */
> > +extern void *dma_alloc_cached(struct device *, size_t, dma_addr_t *,
> > +               gfp_t);
> > +
> >   #define dma_free_writecombine(dev,size,cpu_addr,handle) \
> >          dma_free_coherent(dev,size,cpu_addr,handle)
> >
> > +#define dma_free_cached(dev,size,cpu_addr,handle) \
> > +       dma_free_coherent(dev,size,cpu_addr,handle)
> > +
> >   int dma_mmap_writecombine(struct device *, struct vm_area_struct *,
> >                  void *, dma_addr_t, size_t);
> >
> > +
> > +int dma_mmap_cached(struct device *, struct vm_area_struct *,
> > +               void *, dma_addr_t, size_t);
> > +
> >   /*
> >    * This can be called during boot to increase the size of the consistent
> >    * DMA region above it's default value of 2MB. It must be called before the
> > diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> > index b1911c4..f396ddc 100644
> > --- a/arch/arm/mm/dma-mapping.c
> > +++ b/arch/arm/mm/dma-mapping.c
> > @@ -633,6 +633,20 @@ dma_alloc_writecombine(struct device *dev, size_t size, dma_addr_t *handle, gfp_
> >   }
> >   EXPORT_SYMBOL(dma_alloc_writecombine);
> >
> > +/*
> > + * Allocate a cached DMA region
> > + */
> > +void *
> > +dma_alloc_cached(struct device *dev, size_t size, dma_addr_t *handle, gfp_t gfp)
> > +{
> > +       return __dma_alloc(dev, size, handle, gfp,
> > +                          pgprot_kernel,
> > +                          __builtin_return_address(0));
> > +}
> > +EXPORT_SYMBOL(dma_alloc_cached);
> > +
> > +
> > +
> >   static int dma_mmap(struct device *dev, struct vm_area_struct *vma,
> >                      void *cpu_addr, dma_addr_t dma_addr, size_t size)
> >   {
> > @@ -664,6 +678,13 @@ int dma_mmap_writecombine(struct device *dev, struct vm_area_struct *vma,
> >   }
> >   EXPORT_SYMBOL(dma_mmap_writecombine);
> >
> > +int dma_mmap_cached(struct device *dev, struct vm_area_struct *vma,
> > +                         void *cpu_addr, dma_addr_t dma_addr, size_t size)
> > +{
> > +       return dma_mmap(dev, vma, cpu_addr, dma_addr, size);
> > +}
> > +EXPORT_SYMBOL(dma_mmap_cached);
> > +
> >
> >   /*
> >    * Free a buffer as defined by the above mapping.
> > --
> > 1.7.8.3
> >
> >
> > _______________________________________________
> > Linaro-mm-sig mailing list
> > Linaro-mm-sig@xxxxxxxxxxxxxxxx
> > http://lists.linaro.org/mailman/listinfo/linaro-mm-sig


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