Update alsa interface and gain widget to support linear volume

# Conflicts:
#	src/alsa.c

src/alsa-sim.c

@@ -231,7 +231,7 @@ static void alsa_parse_comment_node(
       err = snd_config_get_integer(node, &dbmin);
       if (err < 0)
         fatal_alsa_error("snd_config_get_integer error", err);
-      elem->min_dB = dbmin / 100;
+      elem->min_cdB = dbmin;
     } else if (strcmp(key, "dbmax") == 0) {
       if (type != SND_CONFIG_TYPE_INTEGER) {
         printf("dbmax type not integer\n");
@@ -241,7 +241,7 @@ static void alsa_parse_comment_node(
       err = snd_config_get_integer(node, &dbmax);
       if (err < 0)
         fatal_alsa_error("snd_config_get_integer error", err);
-      elem->max_dB = dbmax / 100;
+      elem->max_cdB = dbmax;
     }
   }
 }

src/alsa.c

@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 #include <sys/inotify.h>
+#include <alsa/sound/uapi/tlv.h>
 
 #include "alsa.h"
 #include "scarlett2-firmware.h"
@@ -361,7 +362,7 @@ static void alsa_get_elem_tlv(struct alsa_elem *elem) {
   unsigned int tlv[MAX_TLV_RANGE_SIZE];
   unsigned int *dbrec;
   int ret;
-  long min_dB, max_dB;
+  long min_cdB, max_cdB;
 
   snd_ctl_elem_id_alloca(&elem_id);
   snd_ctl_elem_id_set_numid(elem_id, elem->numid);
@@ -370,29 +371,30 @@ static void alsa_get_elem_tlv(struct alsa_elem *elem) {
     elem->card->handle, elem_id, tlv, sizeof(tlv)
   );
   if (ret < 0) {
-    fprintf(stderr, "TLV read error %d\n", ret);
+    fprintf(stderr, "TLV read error: %s\n", snd_strerror(ret));
     return;
   }
 
   ret = snd_tlv_parse_dB_info(tlv, sizeof(tlv), &dbrec);
   if (ret <= 0) {
-    fprintf(stderr, "TLV parse error %d\n", ret);
+    fprintf(stderr, "TLV parse error: %s\n", snd_strerror(ret));
     return;
   }
 
   int min_val = snd_ctl_elem_info_get_min(elem_info);
   int max_val = snd_ctl_elem_info_get_max(elem_info);
 
-  ret = snd_tlv_get_dB_range(tlv, min_val, max_val, &min_dB, &max_dB);
+  ret = snd_tlv_get_dB_range(dbrec, min_val, max_val, &min_cdB, &max_cdB);
   if (ret != 0) {
-    fprintf(stderr, "TLV range error %d\n", ret);
+    fprintf(stderr, "TLV range error: %s\n", snd_strerror(ret));
     return;
   }
 
   elem->min_val = min_val;
   elem->max_val = max_val;
-  elem->min_dB = min_dB / 100;
+  elem->dB_type = dbrec[SNDRV_CTL_TLVO_TYPE];
-  elem->max_dB = max_dB / 100;
+  elem->min_cdB = min_cdB;
+  elem->max_cdB = max_cdB;
 }
 
 static void alsa_get_elem(struct alsa_card *card, int numid) {

src/alsa.h

@@ -126,11 +126,12 @@ struct alsa_elem {
   int         count;
   int         index;
 
-  // for gain/volume elements, the dB range and step
+  // for gain/volume elements, the value range, dB type, and dB range
   int min_val;
   int max_val;
-  int min_dB;
+  int dB_type;
-  int max_dB;
+  int min_cdB;
+  int max_cdB;
 
   // for routing sinks
   int is_routing_snk;

src/widget-gain.c

@@ -4,6 +4,7 @@
 #include "gtkdial.h"
 #include "stringhelper.h"
 #include "widget-gain.h"
+#include "db.h"
 
 struct gain {
   struct alsa_elem *elem;
@@ -56,16 +57,31 @@ static void gain_updated(
 
   char s[20];
   char *p = s;
-  float value = (float)alsa_value * data->scale + elem->min_dB;
+  float value;
+  int min_db = round(elem->min_cdB / 100.0);
+  int max_db = round(elem->max_cdB / 100.0);
 
-  if (value > elem->max_dB)
+  if (elem->dB_type == SND_CTL_TLVT_DB_LINEAR) {
-    value = elem->max_dB;
+    value = linear_value_to_db(
-  else if (value < elem->min_dB)
+      alsa_value,
-    value = elem->min_dB;
+      elem->min_val,
+      elem->max_val,
+      min_db,
+      max_db
+    );
+  } else {
+    value = ((float)(alsa_value - elem->min_val)) * data->scale + (elem->min_cdB / 100.0);
+    if (value > max_db)
+      value = max_db;
+    else if (value < min_db)
+      value = min_db;
+  }
 
-  if (data->zero_is_off && alsa_value == 0) {
+  if (data->zero_is_off && value == min_db) {
     p += sprintf(p, "−∞");
   } else {
+    if (data->scale <= 0.5)
+      value = round(value * 10) / 10;
     if (value < 0)
       p += sprintf(p, "−");
     else if (value > 0)
@@ -159,20 +175,42 @@ GtkWidget *make_gain_alsa_elem(
   gtk_widget_set_valign(data->vbox, GTK_ALIGN_START);
   gtk_widget_set_vexpand(data->vbox, TRUE);
 
-  data->scale = (float)(elem->max_dB - elem->min_dB) /
+  gboolean is_linear = elem->dB_type == SND_CTL_TLVT_DB_LINEAR;
-                       (elem->max_val - elem->min_val);
+  double step;
 
+  if (is_linear) {
+    data->scale = 0.5;
+    step = 0.5;
+  } else {
+    data->scale = (float)(elem->max_cdB - elem->min_cdB) / 100.0 /
+                         (elem->max_val - elem->min_val);
+    step = 1;
+  }
   data->dial = gtk_dial_new_with_range(
     elem->min_val,
     elem->max_val,
-    1,
+    step,
     3 / data->scale
   );
 
   // calculate 0dB value
-  int zero_db_value = (int)((0 - elem->min_dB) / data->scale + elem->min_val);
+  int zero_db_value;
+
+  if (is_linear) {
+    zero_db_value = cdb_to_linear_value(
+      0,
+      elem->min_val,
+      elem->max_val,
+      elem->min_cdB,
+      elem->max_cdB
+    );
+  } else {
+    zero_db_value =
+      (int)((0 - elem->min_cdB) / 100.0 / data->scale + elem->min_val);
+  }
 
   gtk_dial_set_zero_db(GTK_DIAL(data->dial), zero_db_value);
+  gtk_dial_set_is_linear(GTK_DIAL(data->dial), is_linear);
 
   // convert from widget_taper to gtk_dial_taper
   int gtk_dial_taper;