Re: [PATCH 1/8] dma-mapping: add DMA_ATTR_LOW_ADDRESS attribute

[Christoph Hellwig]

>  #define DMA_ATTR_PRIVILEGED		(1UL << 9)
> +/*
> + * DMA_ATTR_LOW_ADDRESS: used to indicate that the buffer should be allocated
> + * at the lowest possible DMA address, usually just at the beginning of the
> + * DMA/IOVA address space ('first-fit' allocation algorithm).
> + */
> +#define DMA_ATTR_LOW_ADDRESS		(1UL << 10)

I think we need better comments explaining that this is best effort
and only applies to DMA API implementations that actually have an
allocatable IOVA space.