On 05/31/2016 07:04 PM, Christoph Hellwig 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.
>>
>> Please have in mind that this is RFC, not finished yet. Only ARM and
>> ARM64 are fixed (and not everywhere).
>> However other API users also have to be converted which is quite
>> intrusive. I would rather avoid it until the overall approach is
>> accepted.
>
> This looks great! Please continue doing the full conversion.
>
>> +/**
>> + * List of possible attributes associated with a DMA mapping. The semantics
>> + * of each attribute should be defined in Documentation/DMA-attributes.txt.
>> + */
>> +#define DMA_ATTR_WRITE_BARRIER BIT(1)
>> +#define DMA_ATTR_WEAK_ORDERING BIT(2)
>> +#define DMA_ATTR_WRITE_COMBINE BIT(3)
>> +#define DMA_ATTR_NON_CONSISTENT BIT(4)
>> +#define DMA_ATTR_NO_KERNEL_MAPPING BIT(5)
>> +#define DMA_ATTR_SKIP_CPU_SYNC BIT(6)
>> +#define DMA_ATTR_FORCE_CONTIGUOUS BIT(7)
>> +#define DMA_ATTR_ALLOC_SINGLE_PAGES BIT(8)
>
> No really for this patch, but I would much prefer to document them next
> to the code in the long run. Also I really think these BIT() macros
> are a distraction compared to the (1 << N) notation.
Not much difference to me but maybe plain number:
... 0x01u
... 0x02u
?
>
>> +/**
>> + * dma_get_attr - check for a specific attribute
>> + * @attr: attribute to look for
>> + * @attrs: attributes to check within
>> + */
>> +static inline bool dma_get_attr(unsigned long attr, unsigned long attrs)
>> +{
>> + return !!(attr & attrs);
>> +}
>
> I'd just kill this helper, much easier to simply open code it in the
> caller.
Keeping it for now helps reducing the number of changes in the patch.
The patch will be quite big as it has to replace all the uses atomically.
I can get rid of the helper in consecutive patch.
Best regards,
Krzysztof
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