Re: [PATCH] asm-generic: add dma-mapping-linear.h

Russell King
2009-06-01T07:51:41Z

On Mon, Jun 01, 2009 at 01:02:42PM +0900, FUJITA Tomonori wrote:
> Where can I find dma_coherent_dev?
>
> I don't fancy this since this is architecture-specific stuff (not
> generic things).

It _is_ very architecture specific. The coherent-ness of devices hardly
depends on the device itself. Eg, PCI devices on x86 are coherent, but
on ARM they aren't.

> > +static inline void
> > +dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
> > + enum dma_data_direction direction)
> > +{
> > + debug_dma_unmap_page(dev, dma_addr, size, direction, true);

Future ARMs will need to do something on unmaps.

> > +static inline void
> > +dma_sync_single_for_cpu(struct device *dev, dma_addr_t dma_handle, size_t size,
> > + enum dma_data_direction direction)
> > +{
> > + debug_dma_sync_single_for_cpu(dev, dma_handle, size, direction);
> > +}
> > +
> > +static inline void
> > +dma_sync_single_range_for_cpu(struct device *dev, dma_addr_t dma_handle,
> > + unsigned long offset, size_t size,
> > + enum dma_data_direction direction)
> > +{
> > + debug_dma_sync_single_range_for_cpu(dev, dma_handle,
> > + offset, size, direction);
> > +}
>
> This looks wrong. You put dma_coherent_dev hook in sync_*_for_device
> but why you don't need it sync_*_for_cpu. It's architecture
> specific. Some need both, some need either, and some need nothing.

If you're non-coherent, you need to implement the sync APIs.

> > +static inline int
> > +dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
> > +{
> > + return 0;

So mappings never fail?

> > +}
> > +
> > +/*
> > + * Return whether the given device DMA address mask can be supported
> > + * properly. For example, if your device can only drive the low 24-bits
> > + * during bus mastering, then you would pass 0x00ffffff as the mask
> > + * to this function.
> > + */
> > +static inline int
> > +dma_supported(struct device *dev, u64 mask)
> > +{
> > + /*
> > + * we fall back to GFP_DMA when the mask isn't all 1s,
> > + * so we can't guarantee allocations that must be
> > + * within a tighter range than GFP_DMA.
> > + */
> > + if (mask < 0x00ffffff)
> > + return 0;
>
> I think that this is pretty architecture specific.

It is - it depends exactly on how you setup the DMA zone and whether
all your RAM is DMA-able.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/