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ALSA: docs: Update MIDI 2.0 documentation for UMP 1.1 enhancement 

There have been a few enhancements for the new UMP 1.1 features.
Update the documentation accordingly.

Link: https://lore.kernel.org/r/20230612081054.17200-11-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2023-06-12 10:10:54 +02:00
parent 01dfa8e969
commit febdfa0e9c
1 changed files with 33 additions and 6 deletions
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39
Documentation/sound/designs/midi-2.0.rst
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@ -68,6 +68,15 @@ default instead of the MIDI 1.0 interface (at altset 0). You can
switch back to the binding with the old MIDI 1.0 interface by passing
`midi2_enable=0` option to snd-usb-audio driver module, too.
The USB audio driver tries to query the UMP Endpoint and UMP Function
Block information that are provided since UMP v1.1, and builds up the
topology based on those information. When the device is older and
doesn't respond to the new UMP inquiries, the driver falls back and
builds the topology based on Group Terminal Block (GTB) information
from the USB descriptor. Some device might be screwed up by the
unexpected UMP command; in such a case, pass `midi2_probe=0` option to
snd-usb-audio driver for skipping the UMP v1.1 inquiries.
When the MIDI 2.0 device is probed, the kernel creates a rawmidi
device for each UMP Endpoint of the device. Its device name is
`/dev/snd/umpC*D*` and different from the standard rawmidi device name
@ -101,11 +110,15 @@ opening `/dev/snd/midiC*D*` will end up with opening the first
substream.
Each UMP Endpoint can provide the additional information, constructed
from USB MIDI 2.0 descriptors. And a UMP Endpoint may contain one or
more UMP Blocks, where UMP Block is an abstraction introduced in the
ALSA UMP implementations to represent the associations among UMP
Groups. UMP Block corresponds to Group Terminal Block (GTB) in USB
MIDI 2.0 specifications but provide a few more generic information.
from the information inquired via UMP 1.1 Stream messages or USB MIDI
2.0 descriptors. And a UMP Endpoint may contain one or more UMP
Blocks, where UMP Block is an abstraction introduced in the ALSA UMP
implementations to represent the associations among UMP Groups. UMP
Block corresponds to Function Block in UMP 1.1 specification. When
UMP 1.1 Function Block information isn't available, it's filled
partially from Group Terminal Block (GTB) as defined in USB MIDI 2.0
specifications.
The information of UMP Endpoints and UMP Blocks are found in the proc
file `/proc/asound/card*/midi*`. For example::
@ -207,6 +220,8 @@ The "MIDI 2.0" port is for a UMP Endpoint, and its difference from
other UMP Group ports is that UMP Endpoint port sends the events from
the all ports on the device ("catch-all"), while each UMP Group port
sends only the events from the given UMP Group.
Also, UMP groupless messages (such as the UMP message type 0x0f) are
sent only to the UMP Endpoint port.
Note that, although each UMP sequencer client usually creates 16
ports, those ports that don't belong to any UMP Blocks (or belonging
@ -273,6 +288,11 @@ Rawmidi API Extensions
The direction is either `SNDRV_UMP_DIR_INPUT`,
`SNDRV_UMP_DIR_OUTPUT` or `SNDRV_UMP_DIR_BIDIRECTION`.
* For the device supports UMP v1.1, the UMP MIDI protocol can be
switched via "Stream Configuration Request" message (UMP type 0x0f,
status 0x05). When UMP core receives such a message, it updates the
UMP EP info and the corresponding sequencer clients as well.
Control API Extensions
======================
@ -337,7 +357,7 @@ Sequencer API Extensions
`group_filter` bitmap. The filter consists of bitmap from 1-based
Group numbers. For example, when the bit 1 is set, messages from
Group 1 (i.e. the very first group) are filtered and not delivered.
The bit 0 is reserved for future use.
The bit 0 is used for filtering UMP groupless messages.
* Two new ioctls are added for UMP-capable clients:
`SNDRV_SEQ_IOCTL_GET_CLIENT_UMP_INFO` and
@ -349,3 +369,10 @@ Sequencer API Extensions
For an Endpoint data, pass 0 to the `type` field, while for a Block
data, pass the block number + 1 to the `type` field.
Setting the data for a kernel client shall result in an error.
* With UMP 1.1, Function Block information may be changed
dynamically. When the update of Function Block is received from the
device, ALSA sequencer core changes the corresponding sequencer port
name and attributes accordingly, and notifies the changes via the
announcement to the ALSA sequencer system port, similarly like the
normal port change notification.