ARM: dts: bcm2712-rpi: Set a 1GB ZONE_DMA limit #5658
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The arm64 initialisation uses the physical address reachable by all DMA controllers to set the size of ZONE_DMA. This fails on BCM2712 with the current dts files because the declaration of the I/O space fools it into thinking the legacy 30-bit DMA channels can see most of the 32-bit space. Take advantage of the simple nature of the implementation by adding a node with a restricted dma-ranges property solely so as to act as the limiting factor in the calculation. See: raspberrypi#5470 Signed-off-by: Phil Elwell <[email protected]>
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I'm slightly concerned that this may be unnecessarily restrictive for Pi 5 most of the time - is the old DWC_OTG block the only block still (sometimes) in use that can only address the first 1GB? - but let's give this some wider testing. |
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I can't think of anything else limited to 1GB (apart from VC). |
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Are you OK with this being merged, or would you rather tie it to dwc_otg use in some way? |
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What exactly does this change affect? |
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DMA-coherent buffers will have to be in the bottom 1GB.
CMA is going to contend for the same space, exactly as we've seen on Pi 4.
In 64-bit mode the kernel has a large reach so although the kmalloc heap
may move it should make no difference.
…On Wed, 18 Oct 2023 at 14:30, popcornmix ***@***.***> wrote:
What exactly does this change affect?
I assume some buffers were more freely allocated before this, and are now
limited to bottom 1GB?
Does this affect cma? dmabufs? kmalloc?
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This is likely to be superseded by #5661. |
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The arm64 initialisation uses the physical address reachable by all DMA controllers to set the size of ZONE_DMA. This fails on BCM2712 with the current dts files because the declaration of the I/O space fools it into thinking the legacy 30-bit DMA channels can see most of the 32-bit space.
Take advantage of the simple nature of the implementation by adding a node with a restricted dma-ranges property solely so as to act as the limiting factor in the calculation.
See: #5470