firmware: cs_dsp: cs_dsp_coeff_write_ctrl() should report changed

ALSA callers need to know whether there was a change to the value so
that they can report a control write change correctly.
Signed-off-by: Simon Trimmer <simont@opensource.cirrus.com>
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20221123165811.3014472-2-rf@opensource.cirrus.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/firmware/cirrus/cs_dsp.c

@@ -752,7 +752,7 @@ static int cs_dsp_coeff_write_ctrl_raw(struct cs_dsp_coeff_ctl *ctl,
  *
  * Must be called with pwr_lock held.
  *
- * Return: Zero for success, a negative number on error.
+ * Return: < 0 on error, 1 when the control value changed and 0 when it has not.
  */
 int cs_dsp_coeff_write_ctrl(struct cs_dsp_coeff_ctl *ctl,
 			    unsigned int off, const void *buf, size_t len)
@@ -767,16 +767,23 @@ int cs_dsp_coeff_write_ctrl(struct cs_dsp_coeff_ctl *ctl,
 	if (len + off * sizeof(u32) > ctl->len)
 		return -EINVAL;
 
-	if (ctl->flags & WMFW_CTL_FLAG_VOLATILE)
+	if (ctl->flags & WMFW_CTL_FLAG_VOLATILE) {
 		ret = -EPERM;
-	else if (buf != ctl->cache)
-		memcpy(ctl->cache + off * sizeof(u32), buf, len);
+	} else if (buf != ctl->cache) {
+		if (memcmp(ctl->cache + off * sizeof(u32), buf, len))
+			memcpy(ctl->cache + off * sizeof(u32), buf, len);
+		else
+			return 0;
+	}
 
 	ctl->set = 1;
 	if (ctl->enabled && ctl->dsp->running)
 		ret = cs_dsp_coeff_write_ctrl_raw(ctl, off, buf, len);
 
-	return ret;
+	if (ret < 0)
+		return ret;
+
+	return 1;
 }
 EXPORT_SYMBOL_GPL(cs_dsp_coeff_write_ctrl);