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dt-bindings: iio: adc: mcp320x: Update for mcp3550/1/3

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All chips supported by this driver clock data out on the falling edge
and latch data in on the rising edge, hence SPI mode (0,0) or (1,1)
must be used.

Furthermore, none of the chips has an internal reference voltage
regulator, so an external supply is always required and needs to be
specified in the device tree lest the IIO "scale" in sysfs cannot be
calculated.

Document these requirements in the device tree binding, add compatible
strings for the newly supported mcp3550/1/3 and explain that SPI mode
(0,0) should be preferred for these chips.

Cc: Mathias Duckeck <m.duckeck@kunbus.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Lukas Wunner 2017-09-09 20:32:41 +02:00 committed by Jonathan Cameron
parent 5e3c3e3382
commit fd060b3cd5
1 changed files with 14 additions and 0 deletions
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14
Documentation/devicetree/bindings/iio/adc/mcp320x.txt
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@ -29,15 +29,29 @@ Required properties:
"microchip,mcp3204"
"microchip,mcp3208"
"microchip,mcp3301"
"microchip,mcp3550-50"
"microchip,mcp3550-60"
"microchip,mcp3551"
"microchip,mcp3553"
NOTE: The use of the compatibles with no vendor prefix
is deprecated and only listed because old DT use them.
- spi-cpha, spi-cpol (boolean):
Either SPI mode (0,0) or (1,1) must be used, so specify
none or both of spi-cpha, spi-cpol. The MCP3550/1/3
is more efficient in mode (1,1) as only 3 instead of
4 bytes need to be read from the ADC, but not all SPI
masters support it.
- vref-supply: Phandle to the external reference voltage supply.
Examples:
spi_controller {
mcp3x0x@0 {
compatible = "mcp3002";
reg = <0>;
spi-max-frequency = <1000000>;
vref-supply = <&vref_reg>;
};
};