[PATCH v3 4/4] hw/misc/pca9552: Trace LED change events

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

Emit a trace event when a LED change its value.

Example booting obmc-phosphor-image:

  $ qemu-system-arm -M witherspoon-bmc -trace pca9552_led_change
  23367@1592575218.896117:pca9552_led_change 0x557cb6896d80 LED id:0 status: 0 -> 1
  23367@1592575218.897072:pca9552_led_change 0x557cb6896d80 LED id:1 status: 0 -> 1
  23367@1592575218.897487:pca9552_led_change 0x557cb6896d80 LED id:2 status: 0 -> 1
  23367@1592575218.897855:pca9552_led_change 0x557cb6896d80 LED id:3 status: 0 -> 1
  23367@1592575218.898256:pca9552_led_change 0x557cb6896d80 LED id:13 status: 0 -> 1
  23367@1592575218.898663:pca9552_led_change 0x557cb6896d80 LED id:14 status: 0 -> 1
  23367@1592575218.899138:pca9552_led_change 0x557cb6896d80 LED id:15 status: 0 -> 1
  23367@1592575281.593379:pca9552_led_change 0x557cb6896d80 LED id:14 status: 1 -> 0
  23367@1592575282.102994:pca9552_led_change 0x557cb6896d80 LED id:14 status: 0 -> 1
  23367@1592575282.613558:pca9552_led_change 0x557cb6896d80 LED id:14 status: 1 -> 0
  23367@1592575283.122774:pca9552_led_change 0x557cb6896d80 LED id:14 status: 0 -> 1

We notice the LED #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

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.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 50c149077d..096ec3112a 100644
--- a/hw/misc/pca9552.c
+++ b/hw/misc/pca9552.c
@@ -62,6 +62,16 @@ static void pca9552_update_pin_input(PCA9552State *s)
     }
 }
 
+static void pca9552_update_led(PCA9552State *s, unsigned id, unsigned new_state)
+{
+    /*
+     * 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_pca9552_led_change(s, id, !new_state, new_state);
+}
+
 static void pca9552_display_leds(PCA9552State *s)
 {
     uint16_t leds_status, led_changed;
@@ -86,6 +96,11 @@ static void pca9552_display_leds(PCA9552State *s)
         buf[i] = '\0';
         trace_pca9552_leds_status(s, buf);
     }
+    for (i = 0; i < s->nr_leds; i++) {
+        if (extract32(led_changed, i, 1)) {
+            pca9552_update_led(s, i, extract32(leds_status, i, 1));
+        }
+    }
 }
 
 static uint8_t pca9552_read(PCA9552State *s, uint8_t reg)
diff --git a/hw/misc/trace-events b/hw/misc/trace-events
index 5d9505ad0f..29892c8b28 100644
--- a/hw/misc/trace-events
+++ b/hw/misc/trace-events
@@ -209,3 +209,4 @@ grlib_apb_pnp_read(uint64_t addr, uint32_t value) "APB PnP read addr:0x%03"PRIx6
 
 # pca9552.c
 pca9552_leds_status(void *object, const char *buf) "%p LEDs 0-15 [%s]"
+pca9552_led_change(void *object, unsigned id, unsigned prev_state, unsigned current_state) "%p LED id:%u status: %u -> %u"
-- 
2.21.3