On 10/01/18 15:32, Christoph Hellwig wrote:
On Wed, Jan 10, 2018 at 11:49:34AM +0000, Robin Murphy wrote:+#ifdef CONFIG_ZONE_DMA + if (mask < DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)) + return 0; +#else + /* + * Because 32-bit DMA masks are so common we expect every architecture + * 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 < DMA_BIT_MASK(32)) + return 0;Do you think it's worth the effort to be a little more accommodating here? i.e.: return dma_max_pfn(dev) >= max_pfn; We seem to have a fair few 28-31 bit masks for older hardware which probably associates with host systems packing equivalently small amounts of RAM.And those devices don't have a ZONE_DMA? I think we could do something like that, but I'd rather have it as a separate commit with a good explanation. Maybe you can just send on on top of the series?
Good point - other than the IXP4xx platform and possibly the Broadcom network drivers, it's probably only x86-relevant stuff where the concern is moot. Let's just keep the simple assumption then, until actually proven otherwise.
Robin. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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