On Tue, 2019-10-08 at 20:03 -0500, Rob Herring wrote: > 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. Yes, you're right, I hadn't thought of it from that perspective. Thanks! > 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? There is no need at all indeed. With that, Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx> and Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx> On a Raspberry Pi 4 with pcie-brcmstb.c which is still work in progress but depends on this. Regards, Nicolas
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