ASoC: doc: dapm: update section "DAPM Widget Events"

The example in this section is not in the kernel sources anymore. Replace
it with an up to date code fragment. Reword the initial paragraph. Remove
"Please" which is not standard practice in documentation.

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://lore.kernel.org/r/20240426-dapm-docs-v2-11-87b07547eb5b@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: lucaceresoli

Documentation/sound/soc/dapm.rst

@@ -376,23 +376,29 @@ jacks can also be switched OFF.
 DAPM Widget Events
 ==================
 
-Some widgets can register their interest with the DAPM core in PM events.
-e.g. A Speaker with an amplifier registers a widget so the amplifier can be
-powered only when the spk is in use.
-::
+Widgets needing to implement a more complex behaviour than what DAPM can do
+can set a custom "event handler" by setting a function pointer. An example
+is a power supply needing to enable a GPIO::
 
-  /* turn speaker amplifier on/off depending on use */
-  static int corgi_amp_event(struct snd_soc_dapm_widget *w, int event)
+  static int sof_es8316_speaker_power_event(struct snd_soc_dapm_widget *w,
+  					  struct snd_kcontrol *kcontrol, int event)
   {
-	gpio_set_value(CORGI_GPIO_APM_ON, SND_SOC_DAPM_EVENT_ON(event));
-	return 0;
+  	if (SND_SOC_DAPM_EVENT_ON(event))
+  		gpiod_set_value_cansleep(gpio_pa, true);
+  	else
+  		gpiod_set_value_cansleep(gpio_pa, false);
+
+  	return 0;
   }
 
-  /* corgi machine dapm widgets */
-  static const struct snd_soc_dapm_widget wm8731_dapm_widgets =
-	SND_SOC_DAPM_SPK("Ext Spk", corgi_amp_event);
+  static const struct snd_soc_dapm_widget st_widgets[] = {
+  	...
+  	SND_SOC_DAPM_SUPPLY("Speaker Power", SND_SOC_NOPM, 0, 0,
+  			    sof_es8316_speaker_power_event,
+  			    SND_SOC_DAPM_PRE_PMD | SND_SOC_DAPM_POST_PMU),
+  };
 
-Please see soc-dapm.h for all other widgets that support events.
+See soc-dapm.h for all other widgets that support events.
 
 
 Event types