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

Santosh Shilimkar
2014-05-02T15:05:57Z

On Friday 02 May 2014 10:58 AM, Russell King - ARM Linux wrote:
> 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);
>
This looks better. Will udpate with above.

>> 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;
>
Ok..

>> }
>>
>> 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?
>
I haven't. Will check.

>> }
>>
>> 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.
>
ok.

Thanks !!

Regards,
Santosh