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SubjectRe: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size
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[ oops, I should have looked at the replies first, now I see Ben already 
had the same thing to say about #3... ]

On 27/09/18 14:49, Christoph Hellwig wrote:
> On Thu, Sep 27, 2018 at 11:50:14AM +1000, Benjamin Herrenschmidt wrote:
>>> - * to be able to satisfy them - either by not supporting more physical
>>> - * memory, or by providing a ZONE_DMA32. If neither is the case, the
>>> - * architecture needs to use an IOMMU instead of the direct mapping.
>>> - */
>>> - if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
>>> + u64 min_mask;
>>> +
>>> + if (IS_ENABLED(CONFIG_ZONE_DMA))
>>> + min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
>>> + else
>>> + min_mask = min_t(u64, DMA_BIT_MASK(32),
>>> + (max_pfn - 1) << PAGE_SHIFT);
>>> +
>>> + if (mask >= phys_to_dma(dev, min_mask))
>>> return 0;
>>
>> nitpick ... to be completely "correct", I would have written
>>
>> if (IS_ENABLED(CONFIG_ZONE_DMA))
>> min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
>> else
>> min_mask = DMA_BIT_MASK(32);
>>
>> min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
>>
>> In "theory" it's also ok to have a mask < ZONE_DMA_BITS as long as it's
>> big enough to fit all memory :-)
>
> Yeah, we could do that.

FWIW I like it even if just for looking slightly more readable. With
that fixup,

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

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