> My understanding was that the dma-ranges property is responsible for > setting up the inbound ranges of RAM's physical addresses, where PCI > could DMA to/from. As regarding the outbound property, this patch > doesn't change this, and there we have the PCI space split (2 GB of > memory, and 64K of I/O spaces mapped from the 64-bit physical > addresses into 32-bit PCI address space). Am I missing something ?
The PCI memory space doesn't differenciate inbound and outbound. For example, if you take the example of a PCI 2.0 or PCI-X setup (I'm leaving PCI-E alone in the discussion because it's a bit special in that area, but the problem is fundamentally the same), and you have on the PCI bus of that thing a device X configured to respond to MMIO at address, for example, 0x80000000. Now, what happens if another device, let's call it Y, tries to DMA to that same address ? Who will pick up the memory write at address 0x80000000 ? The host controller or device X ? There is no concept of "inbound" here.. it's just a memory cycle to address A that gets decoded by whoever tries to decode it on that bus segment. Thus DMA ranges must -not- overlap areas of memory used for MMIO, it just won't work. > With the default 2GB dma-ranges we just get the following on Katmai > with 4GB of SDRAM installed: Because that is simply not supported at the moment unless we add what I've talked about earlier, ie basically, swiotlb support (which Becky is working on at the moment). You might be able to work around it somewhat if your PCI device supports 64-bit BARs in which case you can set your outbound regions above the 32-bit space. Note that I haven't verified whether the 32-bit linux kernel supports that tho. There used to be issues with >32-bit PCI BARs on 32-bit kernel, at least it wouldn't assign them but that may have been fixed. Another option you can try if you device only does 32-bit BARs but supports 64-bit DMA, is to move the DMA window away from the 32-bit MMIO space. Stick it at 1T or so in PCI space. You might need a little bit of kernel tweaking to make the dma-ops pick that up properly but that shouldnt be too hard. If you really need 32-bit DMA support, you'll have to wait for swiotlb from Becky or work with her in bringing it to powerpc so that we can do bounce buffering for those devices. Ben. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
