On Thu, Jun 26, 2014 at 7:17 PM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote: > On Fri, Jun 27, 2014 at 1:10 AM, Russell King - ARM Linux > <linux@xxxxxxxxxxxxxxxx> wrote: >> On Thu, Jun 26, 2014 at 11:53:20PM +0900, Alexandre Courbot wrote: >>> We don't plan to rely on CMA for too long. IOMMU support is on the way >>> and should make our life easier, although no matter the source of >>> memory, we will still have the issue of the lowmem mappings. >> >> When it comes to DMA memory, talking about lowmem vs highmem is utterly >> meaningless. >> >> The lowmem/highmem split is entirely a software concept and is completely >> adjustable. An extreme example is that you can boot any platform with >> more than 32MB of memory with 32MB of lowmem and the remainder as >> highmem. > > True, but isn't it also the case that all lowmem is already mapped in > the kernel address space, and that re-mapping this memory with > different cache settings (e.g. by creating a WC mapping for user-space > to write into) is undefined on ARM and must be avoided? That is the > issue I was referring to. > dma memory should be removed from the kernel linear map (if needed).. assuming it is allocated w/ dma api's. btw, something I've been wondering for a little while, but haven't had time to investigate. Not sure if this applies to you as well. But seems like I have IOMMU's which can be outer-coherent (snoop L2), but I *think* they are not inner-coherent (L1). No idea if current dma memory code can grok this and only do inner-cache op's.. BR, -R > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
