ALSA: hda - Add reboot notifier

The current snd-hda-intel driver seems blocking the power-off on some
devices like eeepc.  Although this is likely a BIOS problem, we can add
a workaround by disabling IRQ lines before power-off operation.
This patch adds the reboot notifier to achieve it.

The detailed problem description is found in bug#11889:
    http://bugme.linux-foundation.org/show_bug.cgi?id=11889

Tested-by: Luiz Fernando N. Capitulino <lcapitulino@mandriva.com.br>
Cc: stable@kernel.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/hda/hda_intel.c

@@ -45,6 +45,7 @@
 #include <linux/slab.h>
 #include <linux/pci.h>
 #include <linux/mutex.h>
+#include <linux/reboot.h>
 #include <sound/core.h>
 #include <sound/initval.h>
 #include "hda_codec.h"
@@ -397,6 +398,9 @@ struct azx {
 
 	/* for pending irqs */
 	struct work_struct irq_pending_work;
+
+	/* reboot notifier (for mysterious hangup problem at power-down) */
+	struct notifier_block reboot_notifier;
 };
 
 /* driver types */
@@ -1978,6 +1982,28 @@ static int azx_resume(struct pci_dev *pci)
 #endif /* CONFIG_PM */
 
 
+/*
+ * reboot notifier for hang-up problem at power-down
+ */
+static int azx_halt(struct notifier_block *nb, unsigned long event, void *buf)
+{
+	struct azx *chip = container_of(nb, struct azx, reboot_notifier);
+	azx_stop_chip(chip);
+	return NOTIFY_OK;
+}
+
+static void azx_notifier_register(struct azx *chip)
+{
+	chip->reboot_notifier.notifier_call = azx_halt;
+	register_reboot_notifier(&chip->reboot_notifier);
+}
+
+static void azx_notifier_unregister(struct azx *chip)
+{
+	if (chip->reboot_notifier.notifier_call)
+		unregister_reboot_notifier(&chip->reboot_notifier);
+}
+
 /*
  * destructor
  */
@@ -1985,6 +2011,8 @@ static int azx_free(struct azx *chip)
 {
 	int i;
 
+	azx_notifier_unregister(chip);
+
 	if (chip->initialized) {
 		azx_clear_irq_pending(chip);
 		for (i = 0; i < chip->num_streams; i++)
@@ -2348,6 +2376,7 @@ static int __devinit azx_probe(struct pci_dev *pci,
 	pci_set_drvdata(pci, card);
 	chip->running = 1;
 	power_down_all_codecs(chip);
+	azx_notifier_register(chip);
 
 	dev++;
 	return err;