On 13 November 2015 14:00, Arnd Bergmann wrote: > On Friday 13 November 2015 13:03:11 Phil Edworthy wrote: > > > > > > Then pci_device_add() sets the devices coherent_dma_mask to 4GiB > before > > > > calling of_pci_dma_configure(). I assume it does this on the basis that this is > a > > > > good default for PCI drivers that don't call dma_set_mask(). > > > > So if arch_setup_dma_ops() walks up the parents to limit the mask, you'll > hit > > > > this mask. > > > > > > arch_setup_dma_ops() does not walk up the hierarchy, of_dma_configure() > > > does this before calling arch_setup_dma_ops(). The PCI devices start out > > > with the 32-bit mask, but the limit should be whatever PCI host uses. > > Ok, so of_dma_configure() could walk up the tree and restrict the dma > > mask to whatever parents limit it to. Then it could be overridden by > > a dma-ranges entry in the DT node, right? > > No, the dma-ranges properties tell you what the allowed masks are, > this is what of_dma_configure() looks at. Ok, I understand now. > > If so, one problem I can see is PCI controllers already use the > > dma-ranges binding but with 3 address cells since it also specifies > > the PCI address range. > > > > I noticed that of_dma_get_range() skips straight to the parent node. > > Shouldn't it attempt to get the dma-ranges for the device's node > > first? > > No, the dma-ranges explain the capabilities of the bus, this is > what you have to look at. The device itself may have additional > restrictions, but those are what the driver knows based on the > compatibility value when it passes the device specific mask into > dma_set_mask() Ok, this is making sense now. > > I mean most hardware is limited by the peripheral's > > capabilities, not the bus. If fact, of_dma_get_range() gets the number > > of address and size cells from the device node, but gets the dma-ranges > > from the parent. That seems a little odd to me. > > of_dma_get_range() calls of_n_addr_cells()/of_n_size_cells(), which get > the #address-cells/#size-cells property from the parent device (except > for the root, which is special). Right, I should have checked what of_n_addr/size_cell() actually did. > > The only other problem I can see is that currently all PCI drivers can > > try to set their dma mask to 64 bits. At the moment that succeeds > > because there are no checks. > > Right, this is the main bug we need to fix. Yep. > > Until devices using them have their DTs > > updated with dma-ranges, we would be limiting them to a 32 bit mask. I > > guess that's not much of an issue in practice. > > Correct. I've tried to tell everyone about this when they added device > nodes for DMA capable devices. In most cases, they want 32-bit masks > anyway. Thanks for your help & patience, much appreciated! Phil -- 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
