On Tue, Jan 30, 2018 at 10:24:48AM +0100, Arnd Bergmann wrote: > On Tue, Jan 30, 2018 at 8:54 AM, Maxime Ripard > <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Jan 29, 2018 at 03:34:02PM +0100, Arnd Bergmann wrote: > >> On Mon, Jan 29, 2018 at 10:25 AM, Linus Walleij > >> <linus.walleij@xxxxxxxxxx> wrote: > >> > On Mon, Jan 29, 2018 at 9:25 AM, Maxime Ripard > >> > <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote: > >> >> On Sat, Jan 27, 2018 at 05:14:26PM +0100, Linus Walleij wrote: > > >> > >> At one point we had discussed adding a 'dma-masters' property that > >> lists all the buses on which a device can be a dma master, and > >> the respective properties of those masters (iommu, coherency, > >> offset, ...). > >> > >> IIRC at the time we decided that we could live without that complexity, > >> but perhaps we cannot. > > > > Are you talking about this ? > > https://elixir.free-electrons.com/linux/latest/source/Documentation/devicetree/bindings/dma/dma.txt#L41 > > > > It doesn't seem to be related to that issue to me. And in our > > particular cases, all the devices are DMA masters, the RAM is just > > mapped to another address. > > No, that's not the one I was thinking of. The idea at the time was much > more generic, and not limited to dma engines. I don't recall the details, > but I think that Thierry was either involved or made the proposal at the > time. Yeah, I vaguely remember discussing something like this before. A quick search through my inbox yielded these two threads, mostly related to IOMMU but I think there were some mentions about dma-ranges and so on as well. I'll have to dig deeper into those threads to refresh my memories, but I won't get around to it until later today. If someone wants to read up on this in the meantime, here are the links: https://lkml.org/lkml/2014/4/27/346 http://lists.infradead.org/pipermail/linux-arm-kernel/2014-May/257200.html From a quick glance the issue of dma-ranges was something that we hand- waved at the time. Thierry
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