On Sep 9, 2013, at 11:01 AM, Grant Likely wrote: > On Fri, 30 Aug 2013 15:26:24 -0500, Kumar Gala <galak@xxxxxxxxxxxxxx> wrote: >> On Aug 30, 2013, at 7:39 AM, Marek Szyprowski wrote: >>> On 8/30/2013 12:46 AM, Grant Likely wrote: >>>> On Mon, 26 Aug 2013 16:39:18 +0200, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote: >>>>> + - "reserved-memory-region" - compatibility is defined, given >>>>> + region is assigned for exclusive usage for by the respective >>>>> + devices. >>>> >>>> BTW, just so you're aware there is already a binding for marking regions >>>> as reserved. It was recently added to arch/powerpc/kernel/prom.c. >>>> Unfortunately it doesn't look like it got documented. Search for >>>> "reserved-ranges". However, I don't think it blocks your work here. That >>>> binding doesn't provide any way for matching devices to reserved ranges. >>>> It is only for telling the kernel "hands of that memory". >>> >>> ok, good to know. >> >> So I think the most generic compatible should effectively be the same >> as 'reserved-ranges', ie this region shouldn't be touched by the >> kernel. >> >> Than we can build on top of that with more specific compatibles. >> >> I have examples from FSL networking SoCs where we would carve out >> memory for backing storage managed completely by the HW and Linux >> wouldn't need to touch it, however we might have a >> "fsl,qman-backing-store" compat encase we might want some debug code >> in linux to look at the region of memory. >> >> I've got examples at qualcomm where we have shared data structures in >> specific memory regions between different processors that aren't cache >> coherent, so want the memory not to be marked as cacheable by Linux >> when it accesses it. Again we'd have a "qcom,smem" prop on top of the >> "reserved-memory-region". > > I think that is a reasonable approach, and works really well for regions > associated with specific hardware because the hardware driver can be > responsible for wiring it up to CMA or manage the region directly. > Whatever the driver desires to do. > > It still remains what to do for generic regions that any device can use. > As I've previously said, I don't like calling out "CMA" specifically in > the compatible property because that happens to be a Linux > implementation specific details. Two years from now someone may propose > a new allocator that should take over what used to be handled by CMA > (kind of like how CMA may end up taking over from ION).... > > Alright, I've thought about it some more and it probably does make sense > to use an additional compatible string. Marek originally suggested > "linux,contiguous-memory-region". I later suggested "shareable-memory-region", > but that's actually a worse name because it doesn't have any reference > to what the region is for (I was fixating on the kernel being able to > use unallocated pages; but that is also an implementation detail). I > exercise my right to change my mind and agree that contiguous is > appropriate here. But instead of calling out the contiguous allocator, > the binding should specifically lay out the usage model for these > regions. I would change the contiguous-memory binding to state the > following: > Contiguous-memory is a region of general purpose memory from > which large buffers of contiguous memory can be allocated. > Contiguous buffers are often used for DMA buffers. The operating > system may use the memory for any purpose, but must immediately > release the pages if a contiguous buffer is required. > > So the way I read things, the current proposal would be: > > The generic form for do-not-touch memory: > compatible = "reserved-memory"; > - I've dropped '-region' because I think it is redundant > - The kernel will not make use of this memory except for when a driver picks it up > > For contiguous memory: > compatible = "contiguous-memory", "reserved-memory" Hmm.., what's an example of a generic use of this compatible set that isn't linux/CMA specific? > For contiguous memory that Linux will use by default if a specific > region isn't specified. > compatible = "contiguous-memory", "reserved-memory" > linux,default-contiguous-region; > - I stuck with a linux, prefix here because I haven't come up with a > non-linux way to describe this. > > Memory that specific hardware can pick up: > compatible = "qcom,smem", "reserved-memory" > > Nodes with a 'size' property and without a 'reg' property need to have a > region allocated and reserved. The allocated region needs to be cached > somewhere. We could create a data structure for tracking the reserved > regions, or could write it in directly. While I shudder at the thought of > modifying the device tree at runtime by the kernel, it might just be the > sanest implementation at this time. I'd like to see what the > implementation looks like. (Since this is potentially controversial, I > would recommend implementing the exact regions in on patch, and add > dynamically allocated regions as a follow-up patch) curious, what's the example for this situation of not having a 'reg' but having a size? > > As far as proper implementation is concerned, I think it should be > explicit in the binding that the kernel should automatically exclude > anything under the reserved-memory node, regardless of the compatible > value. Merely being a child of the reserved-memory node immediately > means that it is a reserved memory region. > > g. > > -- > 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 -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- 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
