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Date: Thu, 27 Sep 2018 16:07:50 +0100 From: Robin Murphy <robin.murphy@....com> To: Christoph Hellwig <hch@....de>, Benjamin Herrenschmidt <benh@...nel.crashing.org> Cc: iommu@...ts.linux-foundation.org, Marek Szyprowski <m.szyprowski@...sung.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org Subject: Re: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size [ 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@....com>
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