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author | Santosh Shilimkar <santosh.shilimkar@ti.com> | 2014-06-22 15:40:00 -0400 |
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committer | Rob Herring <robh@kernel.org> | 2014-09-26 11:18:05 -0500 |
commit | 0244f8f87ec7e327f7a6e45caaa966820eb3fbeb (patch) | |
tree | 90cfd6aa87e49ca311a7077e0baa8128d5d3bfe7 /Documentation/devicetree/booting-without-of.txt | |
parent | 0f33be009b89d2268e94194dc4fd01a7851b6d51 (diff) | |
download | linux-stable-0244f8f87ec7e327f7a6e45caaa966820eb3fbeb.tar.gz linux-stable-0244f8f87ec7e327f7a6e45caaa966820eb3fbeb.tar.bz2 linux-stable-0244f8f87ec7e327f7a6e45caaa966820eb3fbeb.zip |
dt/documentation: add specification of dma bus information
Recently we introduced the generic device tree infrastructure for couple of DMA
bus parameter, dma-ranges and dma-coherent. Update the documentation so that
its useful for future users.
The "dma-ranges" property is intended to be used for describing the
configuration of DMA bus RAM addresses and its offset w.r.t CPU addresses.
The "dma-coherent" property is intended to be used for identifying devices
supported coherent DMA operations.
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Acked-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Diffstat (limited to 'Documentation/devicetree/booting-without-of.txt')
-rw-r--r-- | Documentation/devicetree/booting-without-of.txt | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt index 1f013bd0d320..77685185cf3b 100644 --- a/Documentation/devicetree/booting-without-of.txt +++ b/Documentation/devicetree/booting-without-of.txt @@ -51,6 +51,8 @@ Table of Contents VIII - Specifying device power management information (sleep property) + IX - Specifying dma bus information + Appendix A - Sample SOC node for MPC8540 @@ -1332,6 +1334,57 @@ reasonably grouped in this manner, then create a virtual sleep controller (similar to an interrupt nexus, except that defining a standardized sleep-map should wait until its necessity is demonstrated). +IX - Specifying dma bus information + +Some devices may have DMA memory range shifted relatively to the beginning of +RAM, or even placed outside of kernel RAM. For example, the Keystone 2 SoC +worked in LPAE mode with 4G memory has: +- RAM range: [0x8 0000 0000, 0x8 FFFF FFFF] +- DMA range: [ 0x8000 0000, 0xFFFF FFFF] +and DMA range is aliased into first 2G of RAM in HW. + +In such cases, DMA addresses translation should be performed between CPU phys +and DMA addresses. The "dma-ranges" property is intended to be used +for describing the configuration of such system in DT. + +In addition, each DMA master device on the DMA bus may or may not support +coherent DMA operations. The "dma-coherent" property is intended to be used +for identifying devices supported coherent DMA operations in DT. + +* DMA Bus master +Optional property: +- dma-ranges: <prop-encoded-array> encoded as arbitrary number of triplets of + (child-bus-address, parent-bus-address, length). Each triplet specified + describes a contiguous DMA address range. + The dma-ranges property is used to describe the direct memory access (DMA) + structure of a memory-mapped bus whose device tree parent can be accessed + from DMA operations originating from the bus. It provides a means of + defining a mapping or translation between the physical address space of + the bus and the physical address space of the parent of the bus. + (for more information see ePAPR specification) + +* DMA Bus child +Optional property: +- dma-ranges: <empty> value. if present - It means that DMA addresses + translation has to be enabled for this device. +- dma-coherent: Present if dma operations are coherent + +Example: +soc { + compatible = "ti,keystone","simple-bus"; + ranges = <0x0 0x0 0x0 0xc0000000>; + dma-ranges = <0x80000000 0x8 0x00000000 0x80000000>; + + [...] + + usb: usb@2680000 { + compatible = "ti,keystone-dwc3"; + + [...] + dma-coherent; + }; +}; + Appendix A - Sample SOC node for MPC8540 ======================================== |