On Thursday 20 March 2014 17:12:43 Ben Dooks wrote: > On 20/03/14 17:09, Arnd Bergmann wrote: > > On Thursday 20 March 2014 16:04:36 Ben Dooks wrote: > >> As a note, if we now boot a Lager with DT on 3.14-rc3 series the USB > >> controllers no longer work with full 2GiB RAM enabled in the device > >> tree. > > > > Did it work before these patches got applied initially? > > It did, but I cannot remember if we where limiting DRAM to 1GiB > or not. I would assume you did, or you happened to never actually use memory higher than that for DMA during tests. > >> Could we work around this by having 1GiB of memory defined in the > >> 32bit memory and then add the rest of the 3GiB from the >32bit > >> area via LPAE? Will the kernel ever try to allocate DMA memory from > >> anything >32bit? > > > > You can solve the case for dma_alloc_coherent() this way, or by > > setting the mask correctly. It won't help you for dma_map_* though, > > which still requires someone to add support for swiotlb or using > > an IOMMU if present. > > We do not have an IOMMU present at the moment. Not sure how > to go about setting a mask on a pci-probed device. Ah, right. The mask is a problem because PCI devices assume that they can do DMA to any 32-bit masked address without calling dma_set_mask. Your trick to describe the system memory at a different physical alias would solve this part. Another option might be to add a quirk in the OHCI/EHCI drivers, if you are able to detect this special case from the PCI IDs. Whether we can allow the PCI host controller to just set a mask is an open question. If we decide to go that route, you should be able to do it using the add_bus() callback in the host controller driver. However, it would be a departure from the normal way of doing PCI DMA, and I can't foresee what the implications would be. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
