On Fri, 2019-08-30 at 15:45 +0100, Catalin Marinas wrote: > On Mon, Aug 26, 2019 at 03:46:52PM +0200, Nicolas Saenz Julienne wrote: > > On Mon, 2019-08-26 at 09:09 +0200, Christoph Hellwig wrote: > > > On Tue, Aug 20, 2019 at 04:58:09PM +0200, Nicolas Saenz Julienne wrote: > > > > Some architectures have platform specific DMA addressing limitations. > > > > This will allow for hardware description code to provide the constraints > > > > in a generic manner, so as for arch code to properly setup it's memory > > > > zones and DMA mask. > > > > > > I know this just spreads the arm code, but I still kinda hate it. > > > > Rob's main concern was finding a way to pass the constraint from HW > > definition > > to arch without widening fdt's architecture specific function surface. I'd > > say > > it's fair to argue that having a generic mechanism makes sense as it'll now > > traverse multiple archs and subsystems. > > > > I get adding globals like this is not very appealing, yet I went with it as > > it > > was the easier to integrate with arm's code. Any alternative suggestions? > > In some discussion with Robin, since it's just RPi4 that we are aware of > having such requirement on arm64, he suggested that we have a permanent > ZONE_DMA on arm64 with a default size of 1GB. It should cover all arm64 > SoCs we know of without breaking the single Image binary. The arch/arm > can use its current mach-* support. > > I may like this more than the proposed early_init_dt_get_dma_zone_size() > here which checks for specific SoCs (my preferred way was to build the > mask from all buses described in DT but I hadn't realised the > complications). Hi Catalin, thanks for giving it a thought. I'll be happy to implement it that way. I agree it's a good compromise. @Christoph, do you still want the patch where I create 'zone_dma_bits'? With a hardcoded ZONE_DMA it's not absolutely necessary. Though I remember you said it was a first step towards being able to initialize dma-direct's min_mask in meminit. Regards, Nicolas
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