89 lines
3.3 KiB
Plaintext
89 lines
3.3 KiB
Plaintext
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* Memory reservations for MSM targets
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Large contiguous allocations (generally sizes greater than 64KB) must be
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allocated from a carved out memory pool. The size of the carved out pools
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is based on the sizes drivers need. To properly size the pools, devices
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must specify the size and type of the memory needed. Any driver wanting to
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allocate contiguous memory should indicate this via device tree bindings:
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Required parameters:
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- qcom,memory-reservation-type: type of memory to be reserved. This is a
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string defined in arch/arm/mach-msm/memory.c
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- qcom,memory-reservation-size: size of memory to be reserved
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Example:
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qcom,a-driver {
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compatible = "qcom,a-driver";
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qcom,memory-reservation-type = "EBI1" /* reserve EBI memory */
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qcom,memory-reservation-size = <0x400000>; /* size 4MB */
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};
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Under some circumstances, it may be necessary to remove a chunk of memory
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from the kernel completely using memblock remove. Note this is different
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than adjusting the memory tags passed in via the bootloader as the virtual
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range is not affected. Any driver needing to remove a block of memory should
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add the appropriate binding:
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Required parameters:
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- qcom,memblock-remove: base and size of block to be removed
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qcom,a-driver {
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compatible = "qcom,a-driver";
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/* Remove 4MB at 0x200000*/
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qcom,memblock-remove = <0x200000 0x400000>;
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};
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In order to ensure memory is only reserved when a driver is actually enabled,
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drivers are required to add EXPORT_COMPAT(<name of compatible string>) some
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where in the driver. For the examples above, the driver must add
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EXPORT_COMPAT("qcom,a-driver") to the driver, similar to EXPORT_SYMBOL.
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The EXPORT_COMPAT is to ensure that memory is only carved out if the
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driver is actually enabled, otherwise the memory will not be used.
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If a reservation is needed that isn't associated directly with any one
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driver, the compatible string "qcom,msm-contig-mem" can be used. For
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example:
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qcom,msm-contig-mem {
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compatible = "qcom,msm-contig-mem";
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qcom,memory-reservation-type = "EBI1";
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qcom,memory-reservation-size = <0x280000>; /* 2.5M EBI1 buffer */
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};
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In order to specify the size and address of the fixed memory which has
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previously been removed the memory-fixed binding can be used. This assumes
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that the region has been removed by a separate memblock-remove property
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present in the device tree.
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Required parameters:
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-qcom,memory-fixed: base and size of the fixed memory region
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qcom,a-driver {
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compatible = "qcom,a-driver";
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/* Fixed Memory region of 4MB at 0x200000*/
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qcom,memory-fixed = <0x200000 0x400000>;
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};
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This region is assumed to be a part of a separate hole that has been removed
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and this binding specifies the fixed location and size of the region within
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that hole.
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Some drivers may only wish to reserve memory from the system. Reserved memory
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is still tracked internally by the Linux page allocator. The memory is reserved
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from the buddy allocator at bootup but may be freed back at a later point in
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time with memblock_free and free_bootmem_late.
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Required parameters:
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-qcom,memblock-reserve: base and size of block to be reserved. Drivers should
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call memblock_is_reserved before attempting to use the base address to ensure
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the memory was completely reserved.
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qcom,a-driver {
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compatible = "qcom,a-driver";
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/* reserve a 4MB region @ 0x200000 for use later */
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qcom,memblock-reserve = <0x200000 0x400000>;
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};
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