[alsa-devel] [RFC/PATCH] control_external: Add ability to specify TLV data.

[Dylan Reid]

Allow external control plugins to provide TLV data.  This allows
user-space pcms to specify dB ranges for controls.

This follows the same model as the ALSA drivers for accessing the
data.  The code is based on that implementation.  The control can
provide static data or a callback.  The data is accessed or modified
in the new snd_ctl_ext_elem_tlv callback.

Rev bump the protocol version to enable checking if an external
control supports TLV.

Signed-off-by: Dylan Reid <dgreid at chromium.org>
---
 include/control_external.h |   17 +++++++++++++++-
 src/control/control_ext.c  |   46 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+), 1 deletions(-)

diff --git a/include/control_external.h b/include/control_external.h
index 7c066cf..5392ea6 100644
--- a/include/control_external.h
+++ b/include/control_external.h
@@ -60,13 +60,16 @@ typedef struct snd_ctl_ext snd_ctl_ext_t;
 typedef struct snd_ctl_ext_callback snd_ctl_ext_callback_t;
 /** Key to access a control pointer */
 typedef unsigned long snd_ctl_ext_key_t;
+/** Callback to handle TLV commands. */
+typedef int (snd_ctl_ext_tlv_rw_t)(snd_ctl_ext_t *ext, snd_ctl_ext_key_t key, int op_flag, unsigned int numid,
+				   unsigned int *tlv, unsigned int tlv_size);
 
 /*
  * Protocol version
  */
 #define SND_CTL_EXT_VERSION_MAJOR	1	/**< Protocol major version */
 #define SND_CTL_EXT_VERSION_MINOR	0	/**< Protocol minor version */
-#define SND_CTL_EXT_VERSION_TINY	0	/**< Protocol tiny version */
+#define SND_CTL_EXT_VERSION_TINY	1	/**< Protocol tiny version */
 /**
  * external plugin protocol version
  */
@@ -122,6 +125,13 @@ struct snd_ctl_ext {
 	 * control handle filled by #snd_ctl_ext_create()
 	 */
 	snd_ctl_t *handle;
+	/**
+	 * optional TLV data for the control.
+	 */
+	union {
+		snd_ctl_ext_tlv_rw_t *c;
+		const unsigned int *p;
+	} tlv;
 
 	int nonblock;			/**< non-block mode; read-only */
 	int subscribed;			/**< events subscribed; read-only */
@@ -245,7 +255,12 @@ typedef enum snd_ctl_ext_access {
 	SND_CTL_EXT_ACCESS_WRITE = (1<<1),
 	SND_CTL_EXT_ACCESS_READWRITE = (3<<0),
 	SND_CTL_EXT_ACCESS_VOLATILE = (1<<2),
+	SND_CTL_EXT_ACCESS_TLV_READ = (1<<4),
+	SND_CTL_EXT_ACCESS_TLV_WRITE = (1<<5),
+	SND_CTL_EXT_ACCESS_TLV_READWRITE = (3<<4),
+	SND_CTL_EXT_ACCESS_TLV_COMMAND = (1<<6),
 	SND_CTL_EXT_ACCESS_INACTIVE = (1<<8),
+	SND_CTL_EXT_ACCESS_TLV_CALLBACK = (1<<28),
 } snd_ctl_ext_access_t;
 
 /**
diff --git a/src/control/control_ext.c b/src/control/control_ext.c
index e20d4f3..0a0b397 100644
--- a/src/control/control_ext.c
+++ b/src/control/control_ext.c
@@ -324,6 +324,51 @@ static int snd_ctl_ext_elem_unlock(snd_ctl_t *handle ATTRIBUTE_UNUSED,
 	return -ENXIO;
 }
 
+static int snd_ctl_ext_elem_tlv(snd_ctl_t *handle, int op_flag,
+				unsigned int numid,
+				unsigned int *tlv, unsigned int tlv_size)
+{
+	snd_ctl_ext_t *ext = handle->private_data;
+	snd_ctl_ext_key_t key;
+	int type, ret;
+	unsigned int access, count, len;
+	snd_ctl_elem_id_t id;
+
+	/* we don't support TLV on protocol ver 1.0.0 or earlier */
+	if (ext->version < SNDRV_PROTOCOL_VERSION(1, 0, 0))
+		return -ENXIO;
+
+	snd_ctl_elem_id_clear(&id);
+	if (numid > 0) {
+		ext->callback->elem_list(ext, numid - 1, &id);
+		id.numid = numid;
+	} else
+		id.numid = 0;
+	key = ext->callback->find_elem(ext, &id);
+
+	if (key == SND_CTL_EXT_KEY_NOT_FOUND)
+		return -ENOENT;
+	ret = ext->callback->get_attribute(ext, key, &type, &access, &count);
+	if (ret < 0)
+		return ret;
+
+	if ((op_flag == 0 && (access & SND_CTL_EXT_ACCESS_TLV_READ) == 0) ||
+	    (op_flag > 0 && (access & SND_CTL_EXT_ACCESS_TLV_WRITE) == 0) ||
+	    (op_flag < 0 && (access & SND_CTL_EXT_ACCESS_TLV_COMMAND) == 0))
+		return -ENXIO;
+	if (access & SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK) {
+		return ext->tlv.c(ext, key, op_flag, numid, tlv, tlv_size);
+	} else {
+		if (op_flag)
+			return -ENXIO;
+		len = ext->tlv.p[1] + 2 * sizeof(unsigned int);
+		if (tlv_size < len)
+			return -ENOMEM;
+		memcpy(tlv, ext->tlv.p, len);
+		return 0;
+	}
+}
+
 static int snd_ctl_ext_next_device(snd_ctl_t *handle ATTRIBUTE_UNUSED,
 				   int *device ATTRIBUTE_UNUSED)
 {
@@ -429,6 +474,7 @@ static const snd_ctl_ops_t snd_ctl_ext_ops = {
 	.element_write = snd_ctl_ext_elem_write,
 	.element_lock = snd_ctl_ext_elem_lock,
 	.element_unlock = snd_ctl_ext_elem_unlock,
+	.element_tlv = snd_ctl_ext_elem_tlv,
 	.hwdep_next_device = snd_ctl_ext_next_device,
 	.hwdep_info = snd_ctl_ext_hwdep_info,
 	.pcm_next_device = snd_ctl_ext_next_device,
-- 
1.7.9.rc0