ASoC: cs42l42: Fix handling of hard reset

Merge series from Stefan Binding <sbinding@opensource.cirrus.com>:

These patches fix 3 problems with hard reset:
1. Ensure a minimum reset pulse width
2. Deal with ACPI overriding the requested default GPIO state
3. Avoid a race condition when hard-resetting a SoundWire peripheral
   that is already enumerated

sound/soc/codecs/cs42l42-sdw.c

@@ -344,6 +344,16 @@ static int cs42l42_sdw_update_status(struct sdw_slave *peripheral,
 	switch (status) {
 	case SDW_SLAVE_ATTACHED:
 		dev_dbg(cs42l42->dev, "ATTACHED\n");
+
+		/*
+		 * The SoundWire core can report stale ATTACH notifications
+		 * if we hard-reset CS42L42 in probe() but it had already been
+		 * enumerated. Reject the ATTACH if we haven't yet seen an
+		 * UNATTACH report for the device being in reset.
+		 */
+		if (cs42l42->sdw_waiting_first_unattach)
+			break;
+
 		/*
 		 * Initialise codec, this only needs to be done once.
 		 * When resuming from suspend, resume callback will handle re-init of codec,
@@ -354,6 +364,16 @@ static int cs42l42_sdw_update_status(struct sdw_slave *peripheral,
 		break;
 	case SDW_SLAVE_UNATTACHED:
 		dev_dbg(cs42l42->dev, "UNATTACHED\n");
+
+		if (cs42l42->sdw_waiting_first_unattach) {
+			/*
+			 * SoundWire core has seen that CS42L42 is not on
+			 * the bus so release RESET and wait for ATTACH.
+			 */
+			cs42l42->sdw_waiting_first_unattach = false;
+			gpiod_set_value_cansleep(cs42l42->reset_gpio, 1);
+		}
+
 		break;
 	default:
 		break;

sound/soc/codecs/cs42l42.c

@@ -2320,7 +2320,26 @@ int cs42l42_common_probe(struct cs42l42_private *cs42l42,
 
 	if (cs42l42->reset_gpio) {
 		dev_dbg(cs42l42->dev, "Found reset GPIO\n");
-		gpiod_set_value_cansleep(cs42l42->reset_gpio, 1);
+
+		/*
+		 * ACPI can override the default GPIO state we requested
+		 * so ensure that we start with RESET low.
+		 */
+		gpiod_set_value_cansleep(cs42l42->reset_gpio, 0);
+
+		/* Ensure minimum reset pulse width */
+		usleep_range(10, 500);
+
+		/*
+		 * On SoundWire keep the chip in reset until we get an UNATTACH
+		 * notification from the SoundWire core. This acts as a
+		 * synchronization point to reject stale ATTACH notifications
+		 * if the chip was already enumerated before we reset it.
+		 */
+		if (cs42l42->sdw_peripheral)
+			cs42l42->sdw_waiting_first_unattach = true;
+		else
+			gpiod_set_value_cansleep(cs42l42->reset_gpio, 1);
 	}
 	usleep_range(CS42L42_BOOT_TIME_US, CS42L42_BOOT_TIME_US * 2);
 

sound/soc/codecs/cs42l42.h

@@ -53,6 +53,7 @@ struct  cs42l42_private {
 	u8 stream_use;
 	bool hp_adc_up_pending;
 	bool suspended;
+	bool sdw_waiting_first_unattach;
 	bool init_done;
 };