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Whilst describing a device and not a bus, simple-mfd is modelled on simple-bus where child nodes are iterated and registered as platform devices. Some complex devices, e.g. the Aspeed LPC controller, can benefit from address space mapping such that child nodes can use the regs property to describe their resource offsets within the multi-function device. Signed-off-by: Andrew Jeffery <andrew@aj.id.au> Acked-by: Rob Herring <robh@kernel.org> Signed-off-by: Lee Jones <lee.jones@linaro.org>
52 lines
1.8 KiB
Plaintext
52 lines
1.8 KiB
Plaintext
Multi-Function Devices (MFD)
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These devices comprise a nexus for heterogeneous hardware blocks containing
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more than one non-unique yet varying hardware functionality.
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A typical MFD can be:
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- A mixed signal ASIC on an external bus, sometimes a PMIC (Power Management
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Integrated Circuit) that is manufactured in a lower technology node (rough
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silicon) that handles analog drivers for things like audio amplifiers, LED
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drivers, level shifters, PHY (physical interfaces to things like USB or
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ethernet), regulators etc.
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- A range of memory registers containing "miscellaneous system registers" also
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known as a system controller "syscon" or any other memory range containing a
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mix of unrelated hardware devices.
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Optional properties:
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- compatible : "simple-mfd" - this signifies that the operating system should
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consider all subnodes of the MFD device as separate devices akin to how
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"simple-bus" indicates when to see subnodes as children for a simple
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memory-mapped bus. For more complex devices, when the nexus driver has to
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probe registers to figure out what child devices exist etc, this should not
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be used. In the latter case the child devices will be determined by the
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operating system.
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- ranges: Describes the address mapping relationship to the parent. Should set
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the child's base address to 0, the physical address within parent's address
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space, and the length of the address map.
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- #address-cells: Specifies the number of cells used to represent physical base
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addresses. Must be present if ranges is used.
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- #size-cells: Specifies the number of cells used to represent the size of an
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address. Must be present if ranges is used.
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Example:
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foo@1000 {
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compatible = "syscon", "simple-mfd";
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reg = <0x01000 0x1000>;
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led@08.0 {
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compatible = "register-bit-led";
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offset = <0x08>;
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mask = <0x01>;
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label = "myled";
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default-state = "on";
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};
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};
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