On Tue, Aug 13, 2013 at 02:08:44PM -0600, Stephen Warren wrote: > On 08/09/2013 05:51 AM, Marek Szyprowski wrote: > > Add device tree support for contiguous and reserved memory regions > > defined in device tree. Initialization is done in 2 steps. First, the > > memory is reserved, what happens very early when only flattened device > > tree is available. Then on device initialization the corresponding cma > > and reserved regions are assigned to each device structure. > > Hmmm. This seems an awful lot like putting SW configuration/policy > information into DT rather than HW description. This feels like a > slippery slope... Isn't this kind of thing better handled by a kernel > command-line option to set up the CMA size? Sorry, you were not part of the in-person discussion since it happened at Linaro Connect in Dublin. The concern is that we really need a way to describe some of these _system_ properties. They're not necessarily hardware properties, but they are well-known and likely properties of the system that is running. I.e. say you have a device with a known screen resolution running some reasonably well-known software stacks/applications that you expect will use a certain amount of graphics memory. Or you know how large your camera sensor is, so you know how much carveout the ISP will need for captures. So defining how large the default carveouts should be is very much a property of this system. We would previously have put these settings in a board file and be done, but now we need a way to describe it. /chosen was proposed, but that's mostly used for things that the sysadmin would adjust (traditionally such as firmware stdin/stdout, etc). /options isn't a good place either. Having them on the command line doesn't really work well, over time we'll start to accumulate cruft there. It's bad enough for some of the devices out there that do it, I'd say. So, for the specific case of memory carveouts, this was suggested as the best way forward. -Olof -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
