On Thu, Nov 21, 2019 at 04:24:57PM +0100, Christoph Hellwig wrote: > 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. Actually. This doesn't apply because the dma-mapping tree doesn't have you zone_dma_bits change. I guess we'll need to wait for the next merge window, or maybe post rc1 if this happens to fix the powerpc problem that Christian reported.
