On Tue, Oct 8, 2019 at 3:52 PM Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx> wrote: > > Hi Rob/Robin, > > On Tue, 2019-10-08 at 14:52 -0500, Rob Herring wrote: > > From: Robin Murphy <robin.murphy@xxxxxxx> > > > > Since the "dma-ranges" property is only valid for a node representing a > > bus, of_dma_get_range() currently assumes the node passed in is a leaf > > representing a device, and starts the walk from its parent. In cases > > like PCI host controllers on typical FDT systems, however, where the PCI > > endpoints are probed dynamically the initial leaf node represents the > > 'bus' itself, and this logic means we fail to consider any "dma-ranges" > > describing the host bridge itself. Rework the logic such that > > of_dma_get_range() also works correctly starting from a bus node > > containing "dma-ranges". > > > > While this does mean "dma-ranges" could incorrectly be in a device leaf > > node, there isn't really any way in this function to ensure that a leaf > > node is or isn't a bus node. > > Sorry, I'm not totally sure if this is what you're pointing out with the last > sentence. But, what about the case of a bus configuring a device which also > happens to be a memory mapped bus (say a PCI platform device). It'll get it's > dma config based on its own dma-ranges which is not what we want. What I was trying to say is we just can't tell if we should be looking in the current node or the parent. 'dma-ranges' in a leaf node can be correct or incorrect. Your example is a bit different. I'm not sure that case is valid or can ever work if it is. It's certainly valid that a PCI bridge's parent has dma-ranges and now we'll actually handle any translation. The bridge itself is not a DMA-capable device, but just passing thru DMA. Do we ever need to know the parent's dma-ranges in that case? Or to put it another way, is looking at anything other than leaf dma-ranges useful? Rob
