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.
> +/**
> + * 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.
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