ALSA: ASoC: Allow codecs to override register display

Some codecs have unusual features in their register maps such as very
large registers representing arrays of coefficients. Support these
codecs in the register cache sysfs file by allowing them to provide a
function register_display() overriding the default output for register
contents.

Also ensure that we don't overflow PAGE_SIZE while writing out the
register dump.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

include/sound/soc.h

@@ -410,6 +410,8 @@ struct snd_soc_codec {
 	void *control_data; /* codec control (i2c/3wire) data */
 	unsigned int (*read)(struct snd_soc_codec *, unsigned int);
 	int (*write)(struct snd_soc_codec *, unsigned int, unsigned int);
+	int (*display_register)(struct snd_soc_codec *, char *,
+				size_t, unsigned int);
 	hw_write_t hw_write;
 	hw_read_t hw_read;
 	void *reg_cache;

sound/soc/soc-core.c

@@ -970,9 +970,29 @@ static ssize_t codec_reg_show(struct device *dev,
 		step = codec->reg_cache_step;
 
 	count += sprintf(buf, "%s registers\n", codec->name);
-	for (i = 0; i < codec->reg_cache_size; i += step)
-		count += sprintf(buf + count, "%2x: %4x\n", i,
-			codec->read(codec, i));
+	for (i = 0; i < codec->reg_cache_size; i += step) {
+		count += sprintf(buf + count, "%2x: ", i);
+		if (count >= PAGE_SIZE - 1)
+			break;
+
+		if (codec->display_register)
+			count += codec->display_register(codec, buf + count,
+							 PAGE_SIZE - count, i);
+		else
+			count += snprintf(buf + count, PAGE_SIZE - count,
+					  "%4x", codec->read(codec, i));
+
+		if (count >= PAGE_SIZE - 1)
+			break;
+
+		count += snprintf(buf + count, PAGE_SIZE - count, "\n");
+		if (count >= PAGE_SIZE - 1)
+			break;
+	}
+
+	/* Truncate count; min() would cause a warning */
+	if (count >= PAGE_SIZE)
+		count = PAGE_SIZE - 1;
 
 	return count;
 }