[PATCH v5 0/3] Device Tree support for CMA (Contiguous Memory Allocator)

Tomasz Figa t.figa at samsung.com
Fri Aug 9 09:19:42 EDT 2013

Hi Marek,

On Friday 09 of August 2013 13:51:56 Marek Szyprowski wrote:
> 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

We definitely need this and current version looks pretty good to me.

Acked-by: Tomasz Figa <t.figa at samsung.com>

Best regards,

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