From: Philippe Mathieu-Daudé <f4bug@amsat.org>

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>
---
 hw/misc/pca9552.c    | 15 +++++++++++++++
 hw/misc/trace-events |  1 +
 2 files changed, 16 insertions(+)

diff --git a/hw/misc/pca9552.c b/hw/misc/pca9552.c
index 41f8ad213dd..1c3ad57432a 100644
--- a/hw/misc/pca9552.c
+++ b/hw/misc/pca9552.c
@@ -82,6 +82,21 @@ static void pca955x_display_pins_status(PCA955xState *s,
         buf[i] = '\0';
         trace_pca955x_gpio_status(s->description, buf);
     }
+    if (trace_event_get_state_backends(TRACE_PCA955X_GPIO_CHANGE)) {
+        for (i = 0; i < k->pin_count; i++) {
+            if (extract32(pins_changed, i, 1)) {
+                unsigned new_state = extract32(pins_status, i, 1);
+
+                /*
+                 * We display the state using the PCA logic ("active-high").
+                 * This is not the state of the LED, which signal might be
+                 * wired "active-low" on the board.
+                 */
+                trace_pca955x_gpio_change(s->description, i,
+                                          !new_state, new_state);
+            }
+        }
+    }
 }
 
 static void pca955x_update_pin_input(PCA955xState *s)
diff --git a/hw/misc/trace-events b/hw/misc/trace-events
index bd7bd37ea8d..ebea53735c4 100644
--- a/hw/misc/trace-events
+++ b/hw/misc/trace-events
@@ -212,3 +212,4 @@ grlib_apb_pnp_read(uint64_t addr, uint32_t value) "APB PnP read addr:0x%03"PRIx6
 
 # pca9552.c
 pca955x_gpio_status(const char *description, const char *buf) "%s GPIOs 0-15 [%s]"
+pca955x_gpio_change(const char *description, unsigned id, unsigned prev_state, unsigned current_state) "%s GPIO id:%u status: %u -> %u"
-- 
2.20.1