hw/misc/pca9552: Trace GPIO change events

hw/misc/pca9552: Trace GPIO change events

Emit a trace event when a GPIO change its state.

Example booting obmc-phosphor-image:

  $ qemu-system-arm -M witherspoon-bmc -trace pca955x_gpio_change
  1592690552.687372:pca955x_gpio_change pca1 GPIO id:0 status: 0 -> 1
  1592690552.690169:pca955x_gpio_change pca1 GPIO id:1 status: 0 -> 1
  1592690552.691673:pca955x_gpio_change pca1 GPIO id:2 status: 0 -> 1
  1592690552.696886:pca955x_gpio_change pca1 GPIO id:3 status: 0 -> 1
  1592690552.698614:pca955x_gpio_change pca1 GPIO id:13 status: 0 -> 1
  1592690552.699833:pca955x_gpio_change pca1 GPIO id:14 status: 0 -> 1
  1592690552.700842:pca955x_gpio_change pca1 GPIO id:15 status: 0 -> 1
  1592690683.841921:pca955x_gpio_change pca1 GPIO id:14 status: 1 -> 0
  1592690683.861660:pca955x_gpio_change pca1 GPIO id:14 status: 0 -> 1
  1592690684.371460:pca955x_gpio_change pca1 GPIO id:14 status: 1 -> 0
  1592690684.882115:pca955x_gpio_change pca1 GPIO id:14 status: 0 -> 1
  1592690685.391411:pca955x_gpio_change pca1 GPIO id:14 status: 1 -> 0
  1592690685.901391:pca955x_gpio_change pca1 GPIO id:14 status: 0 -> 1
  1592690686.411678:pca955x_gpio_change pca1 GPIO id:14 status: 1 -> 0
  1592690686.921279:pca955x_gpio_change pca1 GPIO id:14 status: 0 -> 1

We notice the GPIO #14 (front-power LED) starts to blink.

This LED is described in the witherspoon device-tree [*]:

  front-power {
      retain-state-shutdown;
      default-state = "keep";
      gpios = <&pca0 14 GPIO_ACTIVE_LOW>;
  };

[*] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/aspeed-bmc-opp-witherspoon.dts?id=b1f9be9392f0#n140

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Cédric Le Goater <clg@kaod.org>
Message-id: 20200623072723.6324-9-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>