Re: [Xen-devel] [RFC v2] dma-mapping: Use unsigned long for dma_attrs

[Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx>]

On 05/31/2016 08:15 PM, Konrad Rzeszutek Wilk wrote:
> On Mon, May 30, 2016 at 01:54:06PM +0200, Krzysztof Kozlowski wrote:
>> The dma-mapping core and the implementations do not change the
>> DMA attributes passed by pointer.  Thus the pointer can point to const
>> data.  However the attributes do not have to be a bitfield. Instead
>> unsigned long will do fine:
>>
>> 1. This is just simpler.  Both in terms of reading the code and setting
>>    attributes.  Instead of initializing local attributes on the stack and
>>    passing pointer to it to dma_set_attr(), just set the bits.
>>
>> 2. It brings safeness and checking for const correctness because the
>>    attributes are passed by value.
> 
> 
> .. why not go the next step a do an enum? Perhaps that should be mentioned
> as part of the description?

These are additive flags so to me this would look a little bit weird:
enum dma_attr {
        DMA_ATTR_WRITE_BARRIER  = 0x1,
        DMA_ATTR_WEAK_ORDERING  = 0x2,
        DMA_ATTR_WRITE_COMBINE  = 0x4,
        DMA_ATTR_NON_CONSISTENT = 0x8,
        ...
}

It doesn't really look like enumeration.

Best regards,
Krzysztof

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