ALSA: usb-audio: make param quirk_flags change-able in runtime

Change its permision from 0644 to 0444, and add runtime processing.

Developers now can change it during sysfs, without rebooting, for
debugging new buggy devices.

Co-developed-by: Takashi Iwai <[e-mail]>
Signed-off-by: Cryolitia PukNgae <[e-mail]>
Signed-off-by: Takashi Iwai <[e-mail]>

sound/usb/card.c

···
 MODULE_PARM_DESC(delayed_register, "Quirk for delayed registration, given by id:iface, e.g. 0123abcd:4.");
 module_param_array(implicit_fb, bool, NULL, 0444);
 MODULE_PARM_DESC(implicit_fb, "Apply generic implicit feedback sync mode.");
-module_param_array(quirk_flags, charp, NULL, 0444);
-MODULE_PARM_DESC(quirk_flags, "Driver quirk bit flags.");
 module_param_named(use_vmalloc, snd_usb_use_vmalloc, bool, 0444);
 MODULE_PARM_DESC(use_vmalloc, "Use vmalloc for PCM intermediate buffers (default: yes).");
 module_param_named(skip_validation, snd_usb_skip_validation, bool, 0444);
 MODULE_PARM_DESC(skip_validation, "Skip unit descriptor validation (default: no).");
+
+/* protects quirk_flags */
+static DEFINE_MUTEX(quirk_flags_mutex);
+
+static int param_set_quirkp(const char *val,
+			    const struct kernel_param *kp)
+{
+	guard(mutex)(&quirk_flags_mutex);
+	return param_set_charp(val, kp);
+}
+
+static const struct kernel_param_ops param_ops_quirkp = {
+	.set = param_set_quirkp,
+	.get = param_get_charp,
+	.free = param_free_charp,
+};
+
+#define param_check_quirkp param_check_charp
+
+module_param_array(quirk_flags, quirkp, NULL, 0644);
+MODULE_PARM_DESC(quirk_flags, "Add/modify USB audio quirks");
 
 /*
  * we keep the snd_usb_audio_t instances by ourselves for merging
···
 static void snd_usb_init_quirk_flags(int idx, struct snd_usb_audio *chip)
 {
 	size_t i;
+
+	guard(mutex)(&quirk_flags_mutex);
 
 	/* old style option found: the position-based integer value */
 	if (quirk_flags[idx] &&