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

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