ALSA: ac97: Treat snd_ac97_bus_ops as const

This is a preliminary patch to allow const for snd_ac97_bus_ops
definitions in each driver's code.  The ops reference is read-only,
hence it can be declared as const for further optimization.

There should be no functional changes by this patch.

Link: https://lore.kernel.org/r/20200103081714.9560-23-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/ac97_codec.h

@@ -197,7 +197,7 @@ struct snd_ac97_bus_ops {
 
 struct snd_ac97_bus {
 	/* -- lowlevel (hardware) driver specific -- */
-	struct snd_ac97_bus_ops *ops;
+	const struct snd_ac97_bus_ops *ops;
 	void *private_data;
 	void (*private_free) (struct snd_ac97_bus *bus);
 	/* --- */
@@ -310,7 +310,8 @@ static inline int ac97_can_spdif(struct snd_ac97 * ac97)
 
 /* functions */
 /* create new AC97 bus */
-int snd_ac97_bus(struct snd_card *card, int num, struct snd_ac97_bus_ops *ops,
+int snd_ac97_bus(struct snd_card *card, int num,
+		 const struct snd_ac97_bus_ops *ops,
 		 void *private_data, struct snd_ac97_bus **rbus);
 /* create mixer controls */
 int snd_ac97_mixer(struct snd_ac97_bus *bus, struct snd_ac97_template *template,

sound/ac97_bus.c

@@ -55,7 +55,7 @@ static bool snd_ac97_check_id(struct snd_ac97 *ac97, unsigned int id,
 int snd_ac97_reset(struct snd_ac97 *ac97, bool try_warm, unsigned int id,
 	unsigned int id_mask)
 {
-	struct snd_ac97_bus_ops *ops = ac97->bus->ops;
+	const struct snd_ac97_bus_ops *ops = ac97->bus->ops;
 
 	if (try_warm && ops->warm_reset) {
 		ops->warm_reset(ac97);

sound/pci/ac97/ac97_codec.c

@@ -1894,7 +1894,8 @@ static int ac97_reset_wait(struct snd_ac97 *ac97, int timeout, int with_modem)
  *
  * Return: Zero if successful, or a negative error code on failure.
  */
-int snd_ac97_bus(struct snd_card *card, int num, struct snd_ac97_bus_ops *ops,
+int snd_ac97_bus(struct snd_card *card, int num,
+		 const struct snd_ac97_bus_ops *ops,
 		 void *private_data, struct snd_ac97_bus **rbus)
 {
 	int err;