[alsa-devel] RFC: new TLV types for dB range with min/max

[Takashi Iwai]

Hi,

while I was checking bug reports regarding USB mixer dB ranges, I found
that my old code might not work always properly.  In usbmixer.c,

	/* USB descriptions contain the dB scale in 1/256 dB unit
	 * while ALSA TLV contains in 1/100 dB unit
	 */
	scale[2] = (convert_signed_value(cval, cval->min) * 100) / 256;
	scale[3] = (convert_signed_value(cval, cval->res) * 100) / 256;

Since the step size may have a rounding error, this can accumulate to
a significant amount at the max value.

A simple way to avoid this is to just give min and max values instead
of min and step values, and interpolate the middle.  For that, I
create two new TLV types.

Why two?  Since the mute bit can't be packed into an integer (the dB
range can be both positive and negative values) unlike the step size,
I provided here both with and without mute, thus two.

The kernel patch is attached below.  This and a patch to usb-audio can
be found in topic/tlv-minmax branch of sound-unstable GIT tree.
  git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-unstable-2.6.git topic/tlv-minmax

I already wrote and test it with the modified alsa-lib, and the result
looks good.

If anyone has suggestions or objections to this, please let me know.


If this change is OK, I'm going to merge this later for the next,
2.6.32 kernel.


thanks,

Takashi

---
From 085f30654175a91c28d2b66b9ea6cceab627fed0 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai at suse.de>
Date: Tue, 16 Jun 2009 13:57:07 +0200
Subject: [PATCH] ALSA: Add new TLV types for dBwith min/max

Add new types for TLV dB scale specified with min/max values instead
of min/step since the resolution can't match always with the one
a device provides.  For example, usb audio devices give 1/256 dB
resolution while ALSA TLV is based on 1/100 dB resolution.
The new min/max types have less problems because the possible
rounding error happens only at min/max.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 include/sound/tlv.h  |   14 ++++++++++++++
 sound/core/vmaster.c |    8 ++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/include/sound/tlv.h b/include/sound/tlv.h
index d136ea2..9fd5b19 100644
--- a/include/sound/tlv.h
+++ b/include/sound/tlv.h
@@ -35,6 +35,8 @@
 #define SNDRV_CTL_TLVT_DB_SCALE	1       /* dB scale */
 #define SNDRV_CTL_TLVT_DB_LINEAR 2	/* linear volume */
 #define SNDRV_CTL_TLVT_DB_RANGE 3	/* dB range container */
+#define SNDRV_CTL_TLVT_DB_MINMAX 4	/* dB scale with min/max */
+#define SNDRV_CTL_TLVT_DB_MINMAX_MUTE 5	/* dB scale with min/max with mute */
 
 #define TLV_DB_SCALE_ITEM(min, step, mute)			\
 	SNDRV_CTL_TLVT_DB_SCALE, 2 * sizeof(unsigned int),	\
@@ -42,6 +44,18 @@
 #define DECLARE_TLV_DB_SCALE(name, min, step, mute) \
 	unsigned int name[] = { TLV_DB_SCALE_ITEM(min, step, mute) }
 
+/* dB scale specified with min/max values instead of step */
+#define TLV_DB_MINMAX_ITEM(min_dB, max_dB)			\
+	SNDRV_CTL_TLVT_DB_MINMAX, 2 * sizeof(unsigned int),	\
+	(min_dB), (max_dB)
+#define TLV_DB_MINMAX_MUTE_ITEM(min_dB, max_dB)			\
+	SNDRV_CTL_TLVT_DB_MINMAX_MUTE, 2 * sizeof(unsigned int),	\
+	(min_dB), (max_dB)
+#define DECLARE_TLV_DB_MINMAX(name, min_dB, max_dB) \
+	unsigned int name[] = { TLV_DB_MINMAX_ITEM(min_dB, max_dB) }
+#define DECLARE_TLV_DB_MINMAX_MUTE(name, min_dB, max_dB) \
+	unsigned int name[] = { TLV_DB_MINMAX_MUTE_ITEM(min_dB, max_dB) }
+
 /* linear volume between min_dB and max_dB (.01dB unit) */
 #define TLV_DB_LINEAR_ITEM(min_dB, max_dB)		    \
 	SNDRV_CTL_TLVT_DB_LINEAR, 2 * sizeof(unsigned int), \
diff --git a/sound/core/vmaster.c b/sound/core/vmaster.c
index 257624b..3b9b550 100644
--- a/sound/core/vmaster.c
+++ b/sound/core/vmaster.c
@@ -353,7 +353,8 @@ static void master_free(struct snd_kcontrol *kcontrol)
  *
  * The optional argument @tlv can be used to specify the TLV information
  * for dB scale of the master control.  It should be a single element
- * with #SNDRV_CTL_TLVT_DB_SCALE type, and should be the max 0dB.
+ * with #SNDRV_CTL_TLVT_DB_SCALE, #SNDRV_CTL_TLV_DB_MINMAX or
+ * #SNDRV_CTL_TLVT_DB_MINMAX_MUTE type, and should be the max 0dB.
  */
 struct snd_kcontrol *snd_ctl_make_virtual_master(char *name,
 						 const unsigned int *tlv)
@@ -384,7 +385,10 @@ struct snd_kcontrol *snd_ctl_make_virtual_master(char *name,
 	kctl->private_free = master_free;
 
 	/* additional (constant) TLV read */
-	if (tlv && tlv[0] == SNDRV_CTL_TLVT_DB_SCALE) {
+	if (tlv &&
+	    (tlv[0] == SNDRV_CTL_TLVT_DB_SCALE ||
+	     tlv[0] == SNDRV_CTL_TLVT_DB_MINMAX ||
+	     tlv[0] == SNDRV_CTL_TLVT_DB_MINMAX_MUTE)) {
 		kctl->vd[0].access |= SNDRV_CTL_ELEM_ACCESS_TLV_READ;
 		memcpy(master->tlv, tlv, sizeof(master->tlv));
 		kctl->tlv.p = master->tlv;
-- 
1.6.3.2