hw/misc/pca9552: Trace GPIO High/Low events

hw/misc/pca9552: Trace GPIO High/Low events

Add a trivial representation of the PCA9552 GPIOs.

Example booting obmc-phosphor-image:

  $ qemu-system-arm -M witherspoon-bmc -trace pca955x_gpio_status
  1592689902.327837:pca955x_gpio_status pca-unspecified GPIOs 0-15 [*...............]
  1592689902.329934:pca955x_gpio_status pca-unspecified GPIOs 0-15 [**..............]
  1592689902.330717:pca955x_gpio_status pca-unspecified GPIOs 0-15 [***.............]
  1592689902.331431:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****............]
  1592689902.332163:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........*..]
  1592689902.332888:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........**.]
  1592689902.333629:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........***]
  1592690032.793289:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........*.*]
  1592690033.303163:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........***]
  1592690033.812962:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........*.*]
  1592690034.323234:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........***]
  1592690034.832922:pca955x_gpio_status pca-unspecified GPIOs 0-15 [****.........*.*]

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

Suggested-by: Cédric Le Goater <clg@kaod.org>
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: 20200623072723.6324-7-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>