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UniPhier System Bus
The UniPhier System Bus is an external bus that connects on-board devices to
the UniPhier SoC. It is a simple (semi-)parallel bus with address, data, and
some control signals. It supports up to 8 banks (chip selects).
Before any access to the bus, the bus controller must be configured; the bus
controller registers provide the control for the translation from the offset
within each bank to the CPU-viewed address. The needed setup includes the base
address, the size of each bank. Optionally, some timing parameters can be
optimized for faster bus access.
- compatible: should be "socionext,uniphier-system-bus".
- reg: offset and length of the register set for the bus controller device.
- #address-cells: should be 2. The first cell is the bank number (chip select).
The second cell is the address offset within the bank.
- #size-cells: should be 1.
- ranges: should provide a proper address translation from the System Bus to
the parent bus.
The address region(s) that can be assigned for the System Bus is implementation
defined. Some SoCs can use 0x00000000-0x0fffffff and 0x40000000-0x4fffffff,
while other SoCs can only use 0x40000000-0x4fffffff. There might be additional
limitations depending on SoCs and the boot mode. The address translation is
arbitrary as long as the banks are assigned in the supported address space with
the required alignment and they do not overlap one another.
For example, it is possible to map:
bank 0 to 0x42000000-0x43ffffff, bank 5 to 0x46000000-0x46ffffff
It is also possible to map:
bank 0 to 0x48000000-0x49ffffff, bank 5 to 0x44000000-0x44ffffff
There is no reason to stick to a particular translation mapping, but the
"ranges" property should provide a "reasonable" default that is known to work.
The software should initialize the bus controller according to it.
compatible = "socionext,uniphier-system-bus";
reg = <0x58c00000 0x400>;
#address-cells = <2>;
#size-cells = <1>;
ranges = <1 0x00000000 0x42000000 0x02000000
5 0x00000000 0x46000000 0x01000000>;
compatible = "smsc,lan9115";
reg = <1 0x01f00000 0x1000>;
interrupts = <0 48 4>
phy-mode = "mii";
compatible = "ns16550a";
reg = <5 0x00200000 0x20>;
interrupts = <0 49 4>
clock-frequency = <12288000>;
In this example,
- the Ethernet device is connected at the offset 0x01f00000 of CS1 and
mapped to 0x43f00000 of the parent bus.
- the UART device is connected at the offset 0x00200000 of CS5 and
mapped to 0x46200000 of the parent bus.