On Saturday 27 February 2010 10:53:50 am David Miller wrote: > From: Robert Hancock <hancockrwd@xxxxxxxxx> > Date: Fri, 26 Feb 2010 21:08:04 -0600 > > > That seems like a reasonable approach to me. Only question is how to > > implement the check for DMA_64BIT. Can we just check page_to_phys on > > each of the pages in the skb to see if it's > 0xffffffff ? Are there > > any architectures where it's more complicated than that? > > On almost every platform it's "more complicated than that". Mildly speaking, I see the real problem now and it is much higher in the software stack than networking.. > This is the whole issue. What matters is the final DMA address and > since we have IOMMUs and the like, it is absolutely not tenable to > solve this by checking physical address attributes. What's more we may not have IOMMU in place which creates really interesting scenarios for HIGHMEM=y and results in all kind of wonderful band-aids in particular device drivers. Having IOMMU (even if it is only a software one, i.e. this would mean swiotlb for x86-32/highmem) always in place would simplify things greatly.. -- Bartlomiej Zolnierkiewicz -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
