>>>> For OF platforms, this is called via of_dma_configure(), that checks >>>> dma-ranges of node that is *parent* for host bridge. Host bridge >>>> currently does not control this at all. >>> >>> We need to think about this a bit. Is it actually the PCI host >>> bridge that limits the ranges here, or the bus that it is connected >>> to. In the latter case, the caller needs to be adapted to handle >>> both. >> >> In r-car case, I'm not sure what is the source of limitation at physical >> level. >> >> pcie-rcar driver configures ranges for PCIe inbound transactions based >> on dma-ranges property in it's device tree node. In the current device >> tree for this platform, that only contains one range and it is in lower >> memory. >> >> NVMe driver tries i/o to kmalloc()ed area. That returns 0x5xxxxxxxx >> addresses here. As a quick experiment, I tried to add second range to >> pcie-rcar's dma-ranges to cover 0x5xxxxxxxx area - but that did not make >> DMA to high addresses working. >> >> My current understanding is that host bridge hardware module can't >> handle inbound transactions to PCI addresses above 4G - and this >> limitations comes from host bridge itself. >> >> I've read somewhere in the lists that pcie-rcar hardware is "32-bit" - >> but I don't remember where, and don't know lowlevel details. Maybe >> somebody from linux-renesas can elaborate? > > Just a guess, but if the inbound translation windows in the host > bridge are wider than 32-bit, the reason for setting up a single > 32-bit window is probably because that is what the parent bus supports.
Well anyway applying patch similar to your's will fix pcie-rcar + nvme case - thus I don't object :) But it can break other cases ... But why do you hook at set_dma_mask() and overwrite mask inside, instead of hooking at dma_supported() and rejecting unsupported mask? I think later is better, because it lets drivers to handle unsupported high-dma case, like documented in DMA-API_HOWTO.
