cy8c95xx - Cypress CY8C95XX I/O expander linux driver

Linux driver support for Cypress CY8C9520 / CY8C9540 / CY8C9560 i2c I/O expanders.

Currently only tested on CY8C9540a.

The driver makes no distinction between the three components, it just declares the maximum theorical number of GPIOs (8x8 bits port = 64 pins) and consider the user knows the platform used / what to do.

Port 0 is GPIO numbers 0 to 7. Port 1 is 8 to 15. Port 2 is 16 to 23. Port 3 is 24 to 31. Port 4 is 32 to 39. Port 5 is 40 to 47. Port 6 is 48 to 55. Port 7 is 56 to 63.

Supported features:

• GPIOs:
  • Direction setting: input / output
  • Input reading
  • Output setting
  • Bidirectional read / write
• Line drive mode:
  • High Z
  • Pull down
  • Pull up
  • Strong push / pull
• Interrupts
• EEPROM:
  • Save current configuration to default
  • Load default configuration to current
  • Restore factory default (does not apply factory config)

UNSUPPORTED features:

• PWMs
• Line drive mode:
  • "Open drain high" (see datasheet)
  • "Open drain low" (see datasheet)
  • "Slow strong" (see datasheet)
• EEPROM:
  • Reading / writing
• Watchdog

Managing default configuration in EEPROM

An attribute is available at "/sys/bus/i2c/devices/<device_identifier>/ee_por_default".

You can write several commands to it:

• save_current: Save current / running device configuration to eeprom default (configuration to be used on power up).
• restore_factory: Restore factory device configuration to eeprom default (configuration to be used on power up, this WILL NOT change current running configuration).
• load_default: Load default device configuration to current / running configuration.

You can read default configuration store in eeprom by simply reading the file.

An helper python script is available to help read default configuration from stdin: decode_por_default.py

Example: restore AND load factory default

echo "restore_factory" > /sys/bus/i2c/devices/1-0020/ee_por_default
echo "load_default" > /sys/bus/i2c/devices/1-0020/ee_por_default

Example: Read default configuration in a human readable manner

python3 /mnt/cy8c95xx/decode_por_default.py < /sys/bus/i2c/devices/1-0020/ee_por_default

DTS example file (raspberry pi zero w)

See cy8c95xx.dts file for latest version.

/dts-v1/;
/plugin/;

/ {
	compatible = "brcm,bcm2708";
	
	fragment@0 {
		target = <&i2c1>;

		__overlay__ {
			status = "okay";
			#address-cells = <1>;
			#size-cells = <0>;
			cy8c95xx: cy8c95xx@20 {
				compatible = "cypress,cy8c95xx";
				reg = <0x20>;
        
				gpio-controller;
				#gpio-cells = <2>;
        
				interrupt-controller;
				interrupt-parent = <&gpio>;
				#interrupt-cells = <2>;
				interrupts = <21 1>;  // 1 = edge rising
			};
		};
	};
};