On Thu, Nov 21, 2019 at 10:26:44AM +0100, Nicolas Saenz Julienne wrote: > Using a mask to represent bus DMA constraints has a set of limitations. > The biggest one being it can only hold a power of two (minus one). The > DMA mapping code is already aware of this and treats dev->bus_dma_mask > as a limit. This quirk is already used by some architectures although > still rare. > > With the introduction of the Raspberry Pi 4 we've found a new contender > for the use of bus DMA limits, as its PCIe bus can only address the > lower 3GB of memory (of a total of 4GB). This is impossible to represent > with a mask. To make things worse the device-tree code rounds non power > of two bus DMA limits to the next power of two, which is unacceptable in > this case. > > In the light of this, rename dev->bus_dma_mask to dev->bus_dma_limit all > over the tree and treat it as such. Note that dev->bus_dma_limit should > contain the higher accesible DMA address. > > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx> I've tentatively added this patch to the dma-mapping tree based on Robins principal approval of the last version. That way tomorrows linux-next run should still pick it up.
