Re: [alsa-devel] [RFC/PATCH v6 03/12] media: Entities, pads and links

[Clemens Ladisch <clemens@ladisch.de>]

I wrote:
> I'll see if I can draw up the ALSA-specific media stuff over the weekend.

Sorry, wrong weekend.

Anyway, below are some remarks and a patch.


* Entity types

TYPE_NODE was renamed to TYPE_DEVICE because "node" sounds like a node
in a graph, which does not distinguish it from other entity types
because all entities are part of the topology graph.  I chose "device"
as this type describes entities that are visible as some device node to
other software.

TYPE_EXT describes entities that represent some interface to the
external world, TYPE_INT those that are internal to the entire device.
(I'm not sure if that distinction is very useful, but TYPE_SUBDEV seems
to be an even more meaningless name.)


ALSA mixer controls are not directly represented; a better fit for the
architecture of actual devices is that one or more mixer controls can be
associated with an entity.  (This can be done with a field of the mixer
control.)


* Entity properties

There needs to be a mechanism to associate meta-information (properties)
with entities.  This information should be optional and extensible, but,
when being handled inside the kernel, doesn't need to be more than
a read-only blob.  I think that something like ALSA's TLV format (used
for mixer controls) can be used here.  (I'm not mentioning the X-word
here, except to note that the "M" stands for "markup".)


* Entity subtypes

EXT_JACK_ANALOG represents any analog audio and/or video connector.
Properties for audio jacks would be jack type (TRS/RCA), color code,
line level, position, etc.

EXT_JACK_DIGITAL represents a digital connector like S/PDIF (coax/
TOSLINK), ADAT, TDIF, or MADI.

EXT_JACK_BUS represents a bus like FireWire and comes from the USB audio
spec.  (I doubt that any devices with this entitiy will ever exist.)

EXT_INSTRUMENT represents something like an e-guitar, keyboard, or MIDI
controller.  (Instrument entities are typically audio sources and MIDI
sources and sinks, but can also be audio sinks.)

EXT_SPEAKER also includes headphones; there might be made a case for
having those as a separate subtype.

EXT_PLAYER represents a device like a CD/DVD/tape player.  Recorders can
also write to that device, so "player" might not be an ideal name.

EXT_BROADCAST represents devices like TV tuners, satellite receivers,
cable tuners, or radios.

INT_SYNTHESIZER converts MIDI to audio.

INT_NOISE_SOURCE comes from the USB audio spec; this is not an attempt
to describe the characteristics of consumer-grade devices :-) , but
represents an internal noise source for level calibration or measurements.

INT_CONTROLS may have multiple independent controls (this is USB's
Feature Unit); INT_EFFECT may have multiple controls that affect one
single algorithm.

INT_CHANNEL_SPLIT/MERGE are needed for HDAudio devices, whose topology
information has only stereo links.


* Entity specifications

While TYPE_DEVICE entities can be identified by their device node, other
entities typcially have just a numeric ID.  For that, it would be useful
to make do without separate identification and let the driver choose the
entity ID.


Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

--- linux/include/linux/media.h
+++ linux/include/linux/media.h
@@ -46,16 +46,36 @@ struct media_device_info {
 #define MEDIA_ENTITY_TYPE_MASK			0x00ff0000
 #define MEDIA_ENTITY_SUBTYPE_MASK		0x0000ffff
 
-#define MEDIA_ENTITY_TYPE_NODE			(1 << MEDIA_ENTITY_TYPE_SHIFT)
-#define MEDIA_ENTITY_TYPE_NODE_V4L		(MEDIA_ENTITY_TYPE_NODE + 1)
-#define MEDIA_ENTITY_TYPE_NODE_FB		(MEDIA_ENTITY_TYPE_NODE + 2)
-#define MEDIA_ENTITY_TYPE_NODE_ALSA		(MEDIA_ENTITY_TYPE_NODE + 3)
-#define MEDIA_ENTITY_TYPE_NODE_DVB		(MEDIA_ENTITY_TYPE_NODE + 4)
+#define MEDIA_ENTITY_TYPE_DEVICE		(1 << MEDIA_ENTITY_TYPE_SHIFT)
+#define MEDIA_ENTITY_TYPE_DEVICE_V4L		(MEDIA_ENTITY_TYPE_DEVICE + 1)
+#define MEDIA_ENTITY_TYPE_DEVICE_FB		(MEDIA_ENTITY_TYPE_DEVICE + 2)
+#define MEDIA_ENTITY_TYPE_DEVICE_DVB		(MEDIA_ENTITY_TYPE_DEVICE + 3)
+#define MEDIA_ENTITY_TYPE_DEVICE_ALSA_PCM	(MEDIA_ENTITY_TYPE_DEVICE + 4)
+#define MEDIA_ENTITY_TYPE_DEVICE_ALSA_MIDI	(MEDIA_ENTITY_TYPE_DEVICE + 5)
 
-#define MEDIA_ENTITY_TYPE_SUBDEV		(2 << MEDIA_ENTITY_TYPE_SHIFT)
-#define MEDIA_ENTITY_TYPE_SUBDEV_SENSOR		(MEDIA_ENTITY_TYPE_SUBDEV + 1)
-#define MEDIA_ENTITY_TYPE_SUBDEV_FLASH		(MEDIA_ENTITY_TYPE_SUBDEV + 2)
-#define MEDIA_ENTITY_TYPE_SUBDEV_LENS		(MEDIA_ENTITY_TYPE_SUBDEV + 3)
+#define MEDIA_ENTITY_TYPE_EXT			(2 << MEDIA_ENTITY_TYPE_SHIFT)
+#define MEDIA_ENTITY_TYPE_EXT_SENSOR		(MEDIA_ENTITY_TYPE_EXT + 1)
+#define MEDIA_ENTITY_TYPE_EXT_FLASH		(MEDIA_ENTITY_TYPE_EXT + 2)
+#define MEDIA_ENTITY_TYPE_EXT_LENS		(MEDIA_ENTITY_TYPE_EXT + 3)
+#define MEDIA_ENTITY_TYPE_EXT_JACK_MIDI		(MEDIA_ENTITY_TYPE_EXT + 4)
+#define MEDIA_ENTITY_TYPE_EXT_JACK_ANALOG	(MEDIA_ENTITY_TYPE_EXT + 5)
+#define MEDIA_ENTITY_TYPE_EXT_JACK_DIGITAL	(MEDIA_ENTITY_TYPE_EXT + 6)
+#define MEDIA_ENTITY_TYPE_EXT_JACK_BUS		(MEDIA_ENTITY_TYPE_EXT + 7)
+#define MEDIA_ENTITY_TYPE_EXT_INSTRUMENT	(MEDIA_ENTITY_TYPE_EXT + 8)
+#define MEDIA_ENTITY_TYPE_EXT_SPEAKER		(MEDIA_ENTITY_TYPE_EXT + 9)
+#define MEDIA_ENTITY_TYPE_EXT_MICROPHONE	(MEDIA_ENTITY_TYPE_EXT + 10)
+#define MEDIA_ENTITY_TYPE_EXT_PLAYER		(MEDIA_ENTITY_TYPE_EXT + 11)
+#define MEDIA_ENTITY_TYPE_EXT_BROADCAST		(MEDIA_ENTITY_TYPE_EXT + 12)
+
+#define MEDIA_ENTITY_TYPE_INT			(3 << MEDIA_ENTITY_TYPE_SHIFT)
+#define MEDIA_ENTITY_TYPE_INT_SYNTHESIZER	(MEDIA_ENTITY_TYPE_INT + 1)
+#define MEDIA_ENTITY_TYPE_INT_NOISE_SOURCE	(MEDIA_ENTITY_TYPE_INT + 2)
+#define MEDIA_ENTITY_TYPE_INT_MIXER		(MEDIA_ENTITY_TYPE_INT + 3)
+#define MEDIA_ENTITY_TYPE_INT_SELECTOR		(MEDIA_ENTITY_TYPE_INT + 4)
+#define MEDIA_ENTITY_TYPE_INT_CONTROLS		(MEDIA_ENTITY_TYPE_INT + 5)
+#define MEDIA_ENTITY_TYPE_INT_EFFECT		(MEDIA_ENTITY_TYPE_INT + 6)
+#define MEDIA_ENTITY_TYPE_INT_CHANNEL_SPLIT	(MEDIA_ENTITY_TYPE_INT + 7)
+#define MEDIA_ENTITY_TYPE_INT_CHANNEL_MERGE	(MEDIA_ENTITY_TYPE_INT + 8)
 
 #define MEDIA_ENTITY_FLAG_DEFAULT		(1 << 0)
 
@@ -72,7 +92,7 @@ struct media_entity_desc {
 	__u32 reserved[4];
 
 	union {
-		/* Node specifications */
+		/* Device specifications */
 		struct {
 			__u32 major;
 			__u32 minor;
@@ -81,11 +101,15 @@ struct media_entity_desc {
 			__u32 major;
 			__u32 minor;
 		} fb;
-		int alsa;
+		struct {
+			__u32 card;
+			__u32 device;
+			__s32 subdevice;
+		} alsa;
 		int dvb;
 
 		/* Sub-device specifications */
 		/* Nothing needed yet */
 		__u8 raw[184];
 	};
 };