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doc: dt: document altera-passive-serial binding 

Describe an altera-passive-serial devicetree entry, required features

Signed-off-by: Joshua Clayton <stillcompiling@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alan Tull <atull@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Joshua Clayton 2017-06-14 10:36:28 -05:00 committed by Greg Kroah-Hartman
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commit f2b56452c4
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Documentation/devicetree/bindings/fpga/altera-passive-serial.txt Normal file
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Altera Passive Serial SPI FPGA Manager
Altera FPGAs support a method of loading the bitstream over what is
referred to as "passive serial".
The passive serial link is not technically SPI, and might require extra
circuits in order to play nicely with other SPI slaves on the same bus.
See https://www.altera.com/literature/hb/cyc/cyc_c51013.pdf
Required properties:
- compatible: Must be one of the following:
"altr,fpga-passive-serial",
"altr,fpga-arria10-passive-serial"
- reg: SPI chip select of the FPGA
- nconfig-gpios: config pin (referred to as nCONFIG in the manual)
- nstat-gpios: status pin (referred to as nSTATUS in the manual)
Optional properties:
- confd-gpios: confd pin (referred to as CONF_DONE in the manual)
Example:
fpga: fpga@0 {
compatible = "altr,fpga-passive-serial";
spi-max-frequency = <20000000>;
reg = <0>;
nconfig-gpios = <&gpio4 9 GPIO_ACTIVE_LOW>;
nstat-gpios = <&gpio4 11 GPIO_ACTIVE_LOW>;
confd-gpios = <&gpio4 12 GPIO_ACTIVE_LOW>;
};