Messages in this thread | | | From | Ian Campbell <> | Date | Tue, 06 Mar 2012 06:39:12 -0800 | Subject | Re: [Pkg-xen-devel] ioatdma: Boot process hangs then reboots when using Xen + Linux 3.2 |
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On Tue, 2012-03-06 at 06:14 -0800, Dan Williams wrote: > [ 9.276817] ioatdma 0000:00:16.4: desc[0]: > (0x300cc7000->0x300cc7040) cookie: 0 flags: 0x2 ctl: 0x29 (op: 0 > int_en: 1 compl: 1) > ... > [ 9.276832] ioatdma 0000:00:16.4: ioat_get_current_completion: > phys_complete: 0xcc7000 > > Thanks, this clearly shows that our descriptors are above 4GB and that > the driver truncates the completion word. > > Is this new behavior for xen?
Xen makes a distinction between physical addresses and DMA addresses and the latter can potentially be anywhere in the machine's real address space while the former is what GFP_KERNEL etc controls.
You are using pci_pool_alloc which is the correct API to use for these things since it's purpose is to handle cases where PHYS != DMA addr by exposing the DMA address to the caller. As part of that you should also be using dma_addr_t for DMA addresses since that is the type which is defined to handle the appropriate DMA address size on the platform.
I think this DMA!=PHYS can also be true of some non-x86 architectures without Xen too but I guess ioat is quite x86 specific? In any case it is wrong, or at least non-portable, to use unsigned long for these addresses even though it happens on x86 that physaddr == dma addr (usually).
Ian.
-- Ian Campbell
Start every day off with a smile and get it over with. -- W. C. Fields
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