Re: [PATCH v3 5/7] ARM: dma: Use dma_pfn_offset for dma address translation

Russell King - ARM Linux
2014-05-02T15:00:01Z

On Thu, Apr 24, 2014 at 11:30:05AM -0400, Santosh Shilimkar wrote:
> diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> index e701a4d..424fda9 100644
> --- a/arch/arm/include/asm/dma-mapping.h
> +++ b/arch/arm/include/asm/dma-mapping.h
> @@ -58,22 +58,35 @@ static inline int dma_set_mask(struct device *dev, u64 mask)
> #ifndef __arch_pfn_to_dma
> static inline dma_addr_t pfn_to_dma(struct device *dev, unsigned long pfn)
> {
> - return (dma_addr_t)__pfn_to_bus(pfn);
> + if (!dev)
> + return (dma_addr_t)__pfn_to_bus(pfn);
> + else
> + return (dma_addr_t)__pfn_to_bus(pfn - dev->dma_pfn_offset);

I really don't trust gcc to do this right, so I think it would be better
to make life easier on the compiler:

if (dev)
pfn -= dev->dma_pfn_offset;
return (dma_addr_t)__pfn_to_bus(pfn);

> static inline unsigned long dma_to_pfn(struct device *dev, dma_addr_t addr)
> {
> - return __bus_to_pfn(addr);
> + if (!dev)
> + return __bus_to_pfn(addr);
> + else
> + return __bus_to_pfn(addr) + dev->dma_pfn_offset;

and:

unsigned long pfn = __bus_to_pfn(addr);

if (dev)
pfn += dev->dma_pfn_offset;

return pfn;

> }
>
> static inline void *dma_to_virt(struct device *dev, dma_addr_t addr)
> {
> - return (void *)__bus_to_virt((unsigned long)addr);
> + if (!dev)
> + return (void *)__bus_to_virt((unsigned long)addr);
> + else
> + return (void *)__bus_to_virt(__pfn_to_bus(dma_to_pfn(dev, addr)));

This is quite horrendous. There's easier ways to do this... I assume
you haven't looked at the assembler resulting from this at all with
stuff like the p2v patching enabled?

> }
>
> static inline dma_addr_t virt_to_dma(struct device *dev, void *addr)
> {
> - return (dma_addr_t)__virt_to_bus((unsigned long)(addr));
> + if (!dev)
> + return (dma_addr_t)__virt_to_bus((unsigned long)(addr));
> + else
> + return pfn_to_dma(dev,
> + __bus_to_pfn(__virt_to_bus((unsigned long)(addr))));

Same here.

--
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.