Device Tree support for CMA (Contiguous Memory Allocator)

Hello,

This is a fifth version of my proposal for device tree integration for reserved memory and Contiguous Memory Allocator. I've fixed issues pointed by Michal Nazarewicz, Rob Herring and Kumar Gala. For more information, please check the change log at the end of the mail.

In fourth version of this patch set, after the comments from Grant Likely I moved back memory region definitions back to /memory node (as it was in the first version of this proposal). I've also extended the code and made it more generic, added support for so called reserved dma memory (special dma memory regions created by dma_alloc_coherent() function, for exclusive usage for dma allocation for the given device).

Just a few words for those who see this code for the first time:

The proposed bindings allows to define contiguous memory regions of specified base address and size. Then, the defined regions can be assigned to the given device(s) by adding a property with a phanle to the defined contiguous memory region. From the device tree perspective that's all. Once the bindings are added, all the memory allocations from dma-mapping subsystem will be served from the defined contiguous memory regions.

Contiguous Memory Allocator is a framework, which lets to provide a large contiguous memory buffers for (usually a multimedia) devices. The contiguous memory is reserved during early boot and then shared with kernel, which is allowed to allocate it for movable pages. Then, when device driver requests a contigouous buffer, the framework migrates movable pages out of contiguous region and gives it to the driver. When device driver frees the buffer, it is added to kernel memory pool again. For more information, please refer to commit c64be2bb1c6eb43c838b2c6d57 ("drivers: add Contiguous Memory Allocator") and d484864dd96e1830e76895 (CMA merge commit).

Why we need device tree bindings for CMA at all?

Older ARM kernels used so called board-based initialization. Those board files contained a definition of all hardware blocks available on the target system and particular kernel and driver software configuration selected by the board maintainer.

In the new approach the board files will be removed completely and Device Tree approach is used to describe all hardware blocks available on the target system. By definition, the bindings should be software independent, so at least in theory it should be possible to use those bindings with other operating systems than Linux kernel.

Reserved memory configuration belongs to the grey area. It might depend on hardware restriction of the board or modules and low-level configuration done by bootloader. Putting reserved and contiguous memory regions to /memory node and having phandles to those regions in the device nodes however matches well with the device-tree typical style of linking devices with other resources like clocks, interrupts, regulators, power domains, etc. This is the main reason to use such approach instead of putting everything to /chosen node as it has been proposed in v2 and v3.

Best regards
Marek Szyprowski
Samsung R&D Institute Poland

Changelog:

v5:
- renamed "contiguous-memory-region" compatibility string to "linux,contiguous-memory-region" (this one is really specific to Linux kernel implementation)
- renamed "dma-memory-region" property to "memory-region" (suggested by Kumar Gala)
- added support for #address-cells, #size-cells for memory regions (thanks to Rob Herring for suggestion)
- removed generic code to scan specific path in flat device tree (cannot be used to fdt one-pass scan based initialization of memory regions
with #address-cells and #size-cells parsing)
- replaced dma_contiguous_set_default_area() and dma_contiguous_add_device() functions with dev_set_cma_area() call

v4: http://thread.gmane.org/gmane.linux.ports.arm.kernel/256491
- corrected Devcie Tree mailing list address (resend)
- moved back contiguous-memory bindings from /chosen/contiguous-memory to /memory nodes as suggested by Grant (see
http://article.gmane.org/gmane.linux.drivers.devicetree/41030
for more details)
- added support for DMA reserved memory with dma_declare_coherent()
- moved code to drivers/of/of_reserved_mem.c
- added generic code to scan specific path in flat device tree

v3: http://thread.gmane.org/gmane.linux.drivers.devicetree/40013/
- fixed issues pointed by Laura and updated documentation

v2: http://thread.gmane.org/gmane.linux.drivers.devicetree/34075
- moved contiguous-memory bindings from /memory to /chosen/contiguous-memory/ node to avoid spreading Linux specific parameters over the whole device tree definitions
- added support for autoconfigured regions (use zero base)
- fixes minor bugs

v1: http://thread.gmane.org/gmane.linux.drivers.devicetree/30111/
- initial proposal

Patch summary:

Marek Szyprowski (3):
drivers: dma-contiguous: clean source code and prepare for device
tree
drivers: of: add initialization code for dma reserved memory
ARM: init: add support for reserved memory defined by device tree

 Documentation/devicetree/bindings/memory.txt |  152 ++++++++++++++++++++
arch/arm/include/asm/dma-contiguous.h        |    1 -
 arch/arm/mm/init.c                           |    3 +
 arch/x86/include/asm/dma-contiguous.h        |    1 -
 drivers/base/dma-contiguous.c                |  119 ++++++----------
 drivers/of/Kconfig                           |    6 +
 drivers/of/Makefile                          |    1 +
 drivers/of/of_reserved_mem.c                 |  197

++++++++++++++++++++++++++ drivers/of/platform.c
| 5 +

 include/asm-generic/dma-contiguous.h         |   28 ----
 include/linux/dma-contiguous.h               |   55 ++++++-
 include/linux/of_reserved_mem.h              |   14 ++
 12 files changed, 475 insertions(+), 107 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/memory.txt
 create mode 100644 drivers/of/of_reserved_mem.c
 delete mode 100644 include/asm-generic/dma-contiguous.h
 create mode 100644 include/linux/of_reserved_mem.h