ALSA: usb-audio: Initialize every feature unit once at probe time

So far we used to read the current value of the mixer element
dynamically at the first access, and the error from a GET_CUR message
is treated as a fatal error (unless QUIRK_IGNORE_CTL_ERROR is set).
It's rather inconvenient, as most of GET_CUR errors are no fatal, and
we can continue operation with assumption of some fixed value.

This patch makes the USB-audio driver to change the behavior at probe
time; now it tries to initialize the current value of each mixer
element that is built from a feature unit (those for typically for
mixer volumes and switches).  When a read failure happens, it tries to
set the known minimum value.  After that point, a cached value is used
always, hence we won't hit GET_CUR message error any longer.

The error from GET_CUR message is still shown as a warning normally,
but only once at the probe time, and it'll keep operating.  If the
message is confirmed to be harmless, it can be shut up by
QUIRK_IGNORE_CTL_ERROR quirk flag, too.

Tested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20211014130636.17860-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 60d394361a436e0b94d5096131324eb2f00ce8a1..4555de9830c5538c2ff626383602303b9ebc1316 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1199,12 +1199,32 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
        }
 }
 
+/* forcibly initialize the current mixer value; if GET_CUR fails, set to
+ * the minimum as default
+ */
+static void init_cur_mix_raw(struct usb_mixer_elem_info *cval, int ch, int idx)
+{
+       int val, err;
+
+       err = snd_usb_get_cur_mix_value(cval, ch, idx, &val);
+       if (!err)
+               return;
+       if (!cval->head.mixer->ignore_ctl_error)
+               usb_audio_warn(cval->head.mixer->chip,
+                              "%d:%d: failed to get current value for ch %d (%d)\n",
+                              cval->head.id, mixer_ctrl_intf(cval->head.mixer),
+                              ch, err);
+       snd_usb_set_cur_mix_value(cval, ch, idx, cval->min);
+}
+
 /*
  * retrieve the minimum and maximum values for the specified control
  */
 static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
                                   int default_min, struct snd_kcontrol *kctl)
 {
+       int i, idx;
+
        /* for failsafe */
        cval->min = default_min;
        cval->max = cval->min + 1;
@@ -1217,7 +1237,6 @@ static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
        } else {
                int minchn = 0;
                if (cval->cmask) {
-                       int i;
                        for (i = 0; i < MAX_CHANNELS; i++)
                                if (cval->cmask & (1 << i)) {
                                        minchn = i + 1;
@@ -1318,6 +1337,19 @@ no_res_check:
                }
        }
 
+       /* initialize all elements */
+       if (!cval->cmask) {
+               init_cur_mix_raw(cval, 0, 0);
+       } else {
+               idx = 0;
+               for (i = 0; i < MAX_CHANNELS; i++) {
+                       if (cval->cmask & (1 << i)) {
+                               init_cur_mix_raw(cval, i + 1, idx);
+                               idx++;
+                       }
+               }
+       }
+
        return 0;
 }