mirror of
https://github.com/torvalds/linux.git
synced 2024-11-16 09:02:00 +00:00
Documentation: soundwire: Add more documentation
This adds documentation for error handling, locking and streams. Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com> Signed-off-by: Sanyog Kale <sanyog.r.kale@intel.com> Signed-off-by: Shreyas NC <shreyas.nc@intel.com> Signed-off-by: Vinod Koul <vkoul@kernel.org>
This commit is contained in:
Sanyog Kale
Vinod Koul
parent
fce45d1142
commit
89634f99a8
65
Documentation/driver-api/soundwire/error_handling.rst
Normal file
65
Documentation/driver-api/soundwire/error_handling.rst
Normal file
@ -0,0 +1,65 @@
|
||||
========================
|
||||
SoundWire Error Handling
|
||||
========================
|
||||
|
||||
The SoundWire PHY was designed with care and errors on the bus are going to
|
||||
be very unlikely, and if they happen it should be limited to single bit
|
||||
errors. Examples of this design can be found in the synchronization
|
||||
mechanism (sync loss after two errors) and short CRCs used for the Bulk
|
||||
Register Access.
|
||||
|
||||
The errors can be detected with multiple mechanisms:
|
||||
|
||||
1. Bus clash or parity errors: This mechanism relies on low-level detectors
|
||||
that are independent of the payload and usages, and they cover both control
|
||||
and audio data. The current implementation only logs such errors.
|
||||
Improvements could be invalidating an entire programming sequence and
|
||||
restarting from a known position. In the case of such errors outside of a
|
||||
control/command sequence, there is no concealment or recovery for audio
|
||||
data enabled by the SoundWire protocol, the location of the error will also
|
||||
impact its audibility (most-significant bits will be more impacted in PCM),
|
||||
and after a number of such errors are detected the bus might be reset. Note
|
||||
that bus clashes due to programming errors (two streams using the same bit
|
||||
slots) or electrical issues during the transmit/receive transition cannot
|
||||
be distinguished, although a recurring bus clash when audio is enabled is a
|
||||
indication of a bus allocation issue. The interrupt mechanism can also help
|
||||
identify Slaves which detected a Bus Clash or a Parity Error, but they may
|
||||
not be responsible for the errors so resetting them individually is not a
|
||||
viable recovery strategy.
|
||||
|
||||
2. Command status: Each command is associated with a status, which only
|
||||
covers transmission of the data between devices. The ACK status indicates
|
||||
that the command was received and will be executed by the end of the
|
||||
current frame. A NAK indicates that the command was in error and will not
|
||||
be applied. In case of a bad programming (command sent to non-existent
|
||||
Slave or to a non-implemented register) or electrical issue, no response
|
||||
signals the command was ignored. Some Master implementations allow for a
|
||||
command to be retransmitted several times. If the retransmission fails,
|
||||
backtracking and restarting the entire programming sequence might be a
|
||||
solution. Alternatively some implementations might directly issue a bus
|
||||
reset and re-enumerate all devices.
|
||||
|
||||
3. Timeouts: In a number of cases such as ChannelPrepare or
|
||||
ClockStopPrepare, the bus driver is supposed to poll a register field until
|
||||
it transitions to a NotFinished value of zero. The MIPI SoundWire spec 1.1
|
||||
does not define timeouts but the MIPI SoundWire DisCo document adds
|
||||
recommendation on timeouts. If such configurations do not complete, the
|
||||
driver will return a -ETIMEOUT. Such timeouts are symptoms of a faulty
|
||||
Slave device and are likely impossible to recover from.
|
||||
|
||||
Errors during global reconfiguration sequences are extremely difficult to
|
||||
handle:
|
||||
|
||||
1. BankSwitch: An error during the last command issuing a BankSwitch is
|
||||
difficult to backtrack from. Retransmitting the Bank Switch command may be
|
||||
possible in a single segment setup, but this can lead to synchronization
|
||||
problems when enabling multiple bus segments (a command with side effects
|
||||
such as frame reconfiguration would be handled at different times). A global
|
||||
hard-reset might be the best solution.
|
||||
|
||||
Note that SoundWire does not provide a mechanism to detect illegal values
|
||||
written in valid registers. In a number of cases the standard even mentions
|
||||
that the Slave might behave in implementation-defined ways. The bus
|
||||
implementation does not provide a recovery mechanism for such errors, Slave
|
||||
or Master driver implementers are responsible for writing valid values in
|
||||
valid registers and implement additional range checking if needed.
|
||||
@ -6,6 +6,9 @@ SoundWire Documentation
|
||||
:maxdepth: 1
|
||||
|
||||
summary
|
||||
stream
|
||||
error_handling
|
||||
locking
|
||||
|
||||
.. only:: subproject
|
||||
|
||||
|
||||
106
Documentation/driver-api/soundwire/locking.rst
Normal file
106
Documentation/driver-api/soundwire/locking.rst
Normal file
@ -0,0 +1,106 @@
|
||||
=================
|
||||
SoundWire Locking
|
||||
=================
|
||||
|
||||
This document explains locking mechanism of the SoundWire Bus. Bus uses
|
||||
following locks in order to avoid race conditions in Bus operations on
|
||||
shared resources.
|
||||
|
||||
- Bus lock
|
||||
|
||||
- Message lock
|
||||
|
||||
Bus lock
|
||||
========
|
||||
|
||||
SoundWire Bus lock is a mutex and is part of Bus data structure
|
||||
(sdw_bus) which is used for every Bus instance. This lock is used to
|
||||
serialize each of the following operations(s) within SoundWire Bus instance.
|
||||
|
||||
- Addition and removal of Slave(s), changing Slave status.
|
||||
|
||||
- Prepare, Enable, Disable and De-prepare stream operations.
|
||||
|
||||
- Access of Stream data structure.
|
||||
|
||||
Message lock
|
||||
============
|
||||
|
||||
SoundWire message transfer lock. This mutex is part of
|
||||
Bus data structure (sdw_bus). This lock is used to serialize the message
|
||||
transfers (read/write) within a SoundWire Bus instance.
|
||||
|
||||
Below examples show how locks are acquired.
|
||||
|
||||
Example 1
|
||||
---------
|
||||
|
||||
Message transfer.
|
||||
|
||||
1. For every message transfer
|
||||
|
||||
a. Acquire Message lock.
|
||||
|
||||
b. Transfer message (Read/Write) to Slave1 or broadcast message on
|
||||
Bus in case of bank switch.
|
||||
|
||||
c. Release Message lock ::
|
||||
|
||||
+----------+ +---------+
|
||||
| | | |
|
||||
| Bus | | Master |
|
||||
| | | Driver |
|
||||
| | | |
|
||||
+----+-----+ +----+----+
|
||||
| |
|
||||
| bus->ops->xfer_msg() |
|
||||
<-------------------------------+ a. Acquire Message lock
|
||||
| | b. Transfer message
|
||||
| |
|
||||
+-------------------------------> c. Release Message lock
|
||||
| return success/error | d. Return success/error
|
||||
| |
|
||||
+ +
|
||||
|
||||
Example 2
|
||||
---------
|
||||
|
||||
Prepare operation.
|
||||
|
||||
1. Acquire lock for Bus instance associated with Master 1.
|
||||
|
||||
2. For every message transfer in Prepare operation
|
||||
|
||||
a. Acquire Message lock.
|
||||
|
||||
b. Transfer message (Read/Write) to Slave1 or broadcast message on
|
||||
Bus in case of bank switch.
|
||||
|
||||
c. Release Message lock.
|
||||
|
||||
3. Release lock for Bus instance associated with Master 1 ::
|
||||
|
||||
+----------+ +---------+
|
||||
| | | |
|
||||
| Bus | | Master |
|
||||
| | | Driver |
|
||||
| | | |
|
||||
+----+-----+ +----+----+
|
||||
| |
|
||||
| sdw_prepare_stream() |
|
||||
<-------------------------------+ 1. Acquire bus lock
|
||||
| | 2. Perform stream prepare
|
||||
| |
|
||||
| |
|
||||
| bus->ops->xfer_msg() |
|
||||
<-------------------------------+ a. Acquire Message lock
|
||||
| | b. Transfer message
|
||||
| |
|
||||
+-------------------------------> c. Release Message lock
|
||||
| return success/error | d. Return success/error
|
||||
| |
|
||||
| |
|
||||
| return success/error | 3. Release bus lock
|
||||
+-------------------------------> 4. Return success/error
|
||||
| |
|
||||
+ +
|
||||
372
Documentation/driver-api/soundwire/stream.rst
Normal file
372
Documentation/driver-api/soundwire/stream.rst
Normal file
@ -0,0 +1,372 @@
|
||||
=========================
|
||||
Audio Stream in SoundWire
|
||||
=========================
|
||||
|
||||
An audio stream is a logical or virtual connection created between
|
||||
|
||||
(1) System memory buffer(s) and Codec(s)
|
||||
|
||||
(2) DSP memory buffer(s) and Codec(s)
|
||||
|
||||
(3) FIFO(s) and Codec(s)
|
||||
|
||||
(4) Codec(s) and Codec(s)
|
||||
|
||||
which is typically driven by a DMA(s) channel through the data link. An
|
||||
audio stream contains one or more channels of data. All channels within
|
||||
stream must have same sample rate and same sample size.
|
||||
|
||||
Assume a stream with two channels (Left & Right) is opened using SoundWire
|
||||
interface. Below are some ways a stream can be represented in SoundWire.
|
||||
|
||||
Stream Sample in memory (System memory, DSP memory or FIFOs) ::
|
||||
|
||||
-------------------------
|
||||
| L | R | L | R | L | R |
|
||||
-------------------------
|
||||
|
||||
Example 1: Stereo Stream with L and R channels is rendered from Master to
|
||||
Slave. Both Master and Slave is using single port. ::
|
||||
|
||||
+---------------+ Clock Signal +---------------+
|
||||
| Master +----------------------------------+ Slave |
|
||||
| Interface | | Interface |
|
||||
| | | 1 |
|
||||
| | Data Signal | |
|
||||
| L + R +----------------------------------+ L + R |
|
||||
| (Data) | Data Direction | (Data) |
|
||||
+---------------+ +-----------------------> +---------------+
|
||||
|
||||
|
||||
Example 2: Stereo Stream with L and R channels is captured from Slave to
|
||||
Master. Both Master and Slave is using single port. ::
|
||||
|
||||
|
||||
+---------------+ Clock Signal +---------------+
|
||||
| Master +----------------------------------+ Slave |
|
||||
| Interface | | Interface |
|
||||
| | | 1 |
|
||||
| | Data Signal | |
|
||||
| L + R +----------------------------------+ L + R |
|
||||
| (Data) | Data Direction | (Data) |
|
||||
+---------------+ <-----------------------+ +---------------+
|
||||
|
||||
|
||||
Example 3: Stereo Stream with L and R channels is rendered by Master. Each
|
||||
of the L and R channel is received by two different Slaves. Master and both
|
||||
Slaves are using single port. ::
|
||||
|
||||
+---------------+ Clock Signal +---------------+
|
||||
| Master +---------+------------------------+ Slave |
|
||||
| Interface | | | Interface |
|
||||
| | | | 1 |
|
||||
| | | Data Signal | |
|
||||
| L + R +---+------------------------------+ L |
|
||||
| (Data) | | | Data Direction | (Data) |
|
||||
+---------------+ | | +-------------> +---------------+
|
||||
| |
|
||||
| |
|
||||
| | +---------------+
|
||||
| +----------------------> | Slave |
|
||||
| | Interface |
|
||||
| | 2 |
|
||||
| | |
|
||||
+----------------------------> | R |
|
||||
| (Data) |
|
||||
+---------------+
|
||||
|
||||
|
||||
Example 4: Stereo Stream with L and R channel is rendered by two different
|
||||
Ports of the Master and is received by only single Port of the Slave
|
||||
interface. ::
|
||||
|
||||
+--------------------+
|
||||
| |
|
||||
| +--------------+ +----------------+
|
||||
| | || | |
|
||||
| | Data Port || L Channel | |
|
||||
| | 1 |------------+ | |
|
||||
| | L Channel || | +-----+----+ |
|
||||
| | (Data) || | L + R Channel || Data | |
|
||||
| Master +----------+ | +---+---------> || Port | |
|
||||
| Interface | | || 1 | |
|
||||
| +--------------+ | || | |
|
||||
| | || | +----------+ |
|
||||
| | Data Port |------------+ | |
|
||||
| | 2 || R Channel | Slave |
|
||||
| | R Channel || | Interface |
|
||||
| | (Data) || | 1 |
|
||||
| +--------------+ Clock Signal | L + R |
|
||||
| +---------------------------> | (Data) |
|
||||
+--------------------+ | |
|
||||
+----------------+
|
||||
|
||||
SoundWire Stream Management flow
|
||||
================================
|
||||
|
||||
Stream definitions
|
||||
------------------
|
||||
|
||||
(1) Current stream: This is classified as the stream on which operation has
|
||||
to be performed like prepare, enable, disable, de-prepare etc.
|
||||
|
||||
(2) Active stream: This is classified as the stream which is already active
|
||||
on Bus other than current stream. There can be multiple active streams
|
||||
on the Bus.
|
||||
|
||||
SoundWire Bus manages stream operations for each stream getting
|
||||
rendered/captured on the SoundWire Bus. This section explains Bus operations
|
||||
done for each of the stream allocated/released on Bus. Following are the
|
||||
stream states maintained by the Bus for each of the audio stream.
|
||||
|
||||
|
||||
SoundWire stream states
|
||||
-----------------------
|
||||
|
||||
Below shows the SoundWire stream states and state transition diagram. ::
|
||||
|
||||
+-----------+ +------------+ +----------+ +----------+
|
||||
| ALLOCATED +---->| CONFIGURED +---->| PREPARED +---->| ENABLED |
|
||||
| STATE | | STATE | | STATE | | STATE |
|
||||
+-----------+ +------------+ +----------+ +----+-----+
|
||||
^
|
||||
|
|
||||
|
|
||||
v
|
||||
+----------+ +------------+ +----+-----+
|
||||
| RELEASED |<----------+ DEPREPARED |<-------+ DISABLED |
|
||||
| STATE | | STATE | | STATE |
|
||||
+----------+ +------------+ +----------+
|
||||
|
||||
NOTE: State transition between prepare and deprepare is supported in Spec
|
||||
but not in the software (subsystem)
|
||||
|
||||
NOTE2: Stream state transition checks need to be handled by caller
|
||||
framework, for example ALSA/ASoC. No checks for stream transition exist in
|
||||
SoundWire subsystem.
|
||||
|
||||
Stream State Operations
|
||||
-----------------------
|
||||
|
||||
Below section explains the operations done by the Bus on Master(s) and
|
||||
Slave(s) as part of stream state transitions.
|
||||
|
||||
SDW_STREAM_ALLOCATED
|
||||
~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Allocation state for stream. This is the entry state
|
||||
of the stream. Operations performed before entering in this state:
|
||||
|
||||
(1) A stream runtime is allocated for the stream. This stream
|
||||
runtime is used as a reference for all the operations performed
|
||||
on the stream.
|
||||
|
||||
(2) The resources required for holding stream runtime information are
|
||||
allocated and initialized. This holds all stream related information
|
||||
such as stream type (PCM/PDM) and parameters, Master and Slave
|
||||
interface associated with the stream, stream state etc.
|
||||
|
||||
After all above operations are successful, stream state is set to
|
||||
``SDW_STREAM_ALLOCATED``.
|
||||
|
||||
Bus implements below API for allocate a stream which needs to be called once
|
||||
per stream. From ASoC DPCM framework, this stream state maybe linked to
|
||||
.startup() operation.
|
||||
|
||||
.. code-block:: c
|
||||
int sdw_alloc_stream(char * stream_name);
|
||||
|
||||
|
||||
SDW_STREAM_CONFIGURED
|
||||
~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Configuration state of stream. Operations performed before entering in
|
||||
this state:
|
||||
|
||||
(1) The resources allocated for stream information in SDW_STREAM_ALLOCATED
|
||||
state are updated here. This includes stream parameters, Master(s)
|
||||
and Slave(s) runtime information associated with current stream.
|
||||
|
||||
(2) All the Master(s) and Slave(s) associated with current stream provide
|
||||
the port information to Bus which includes port numbers allocated by
|
||||
Master(s) and Slave(s) for current stream and their channel mask.
|
||||
|
||||
After all above operations are successful, stream state is set to
|
||||
``SDW_STREAM_CONFIGURED``.
|
||||
|
||||
Bus implements below APIs for CONFIG state which needs to be called by
|
||||
the respective Master(s) and Slave(s) associated with stream. These APIs can
|
||||
only be invoked once by respective Master(s) and Slave(s). From ASoC DPCM
|
||||
framework, this stream state is linked to .hw_params() operation.
|
||||
|
||||
.. code-block:: c
|
||||
int sdw_stream_add_master(struct sdw_bus * bus,
|
||||
struct sdw_stream_config * stream_config,
|
||||
struct sdw_ports_config * ports_config,
|
||||
struct sdw_stream_runtime * stream);
|
||||
|
||||
int sdw_stream_add_slave(struct sdw_slave * slave,
|
||||
struct sdw_stream_config * stream_config,
|
||||
struct sdw_ports_config * ports_config,
|
||||
struct sdw_stream_runtime * stream);
|
||||
|
||||
|
||||
SDW_STREAM_PREPARED
|
||||
~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Prepare state of stream. Operations performed before entering in this state:
|
||||
|
||||
(1) Bus parameters such as bandwidth, frame shape, clock frequency,
|
||||
are computed based on current stream as well as already active
|
||||
stream(s) on Bus. Re-computation is required to accommodate current
|
||||
stream on the Bus.
|
||||
|
||||
(2) Transport and port parameters of all Master(s) and Slave(s) port(s) are
|
||||
computed for the current as well as already active stream based on frame
|
||||
shape and clock frequency computed in step 1.
|
||||
|
||||
(3) Computed Bus and transport parameters are programmed in Master(s) and
|
||||
Slave(s) registers. The banked registers programming is done on the
|
||||
alternate bank (bank currently unused). Port(s) are enabled for the
|
||||
already active stream(s) on the alternate bank (bank currently unused).
|
||||
This is done in order to not disrupt already active stream(s).
|
||||
|
||||
(4) Once all the values are programmed, Bus initiates switch to alternate
|
||||
bank where all new values programmed gets into effect.
|
||||
|
||||
(5) Ports of Master(s) and Slave(s) for current stream are prepared by
|
||||
programming PrepareCtrl register.
|
||||
|
||||
After all above operations are successful, stream state is set to
|
||||
``SDW_STREAM_PREPARED``.
|
||||
|
||||
Bus implements below API for PREPARE state which needs to be called once per
|
||||
stream. From ASoC DPCM framework, this stream state is linked to
|
||||
.prepare() operation.
|
||||
|
||||
.. code-block:: c
|
||||
int sdw_prepare_stream(struct sdw_stream_runtime * stream);
|
||||
|
||||
|
||||
SDW_STREAM_ENABLED
|
||||
~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Enable state of stream. The data port(s) are enabled upon entering this state.
|
||||
Operations performed before entering in this state:
|
||||
|
||||
(1) All the values computed in SDW_STREAM_PREPARED state are programmed
|
||||
in alternate bank (bank currently unused). It includes programming of
|
||||
already active stream(s) as well.
|
||||
|
||||
(2) All the Master(s) and Slave(s) port(s) for the current stream are
|
||||
enabled on alternate bank (bank currently unused) by programming
|
||||
ChannelEn register.
|
||||
|
||||
(3) Once all the values are programmed, Bus initiates switch to alternate
|
||||
bank where all new values programmed gets into effect and port(s)
|
||||
associated with current stream are enabled.
|
||||
|
||||
After all above operations are successful, stream state is set to
|
||||
``SDW_STREAM_ENABLED``.
|
||||
|
||||
Bus implements below API for ENABLE state which needs to be called once per
|
||||
stream. From ASoC DPCM framework, this stream state is linked to
|
||||
.trigger() start operation.
|
||||
|
||||
.. code-block:: c
|
||||
int sdw_enable_stream(struct sdw_stream_runtime * stream);
|
||||
|
||||
SDW_STREAM_DISABLED
|
||||
~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Disable state of stream. The data port(s) are disabled upon exiting this state.
|
||||
Operations performed before entering in this state:
|
||||
|
||||
(1) All the Master(s) and Slave(s) port(s) for the current stream are
|
||||
disabled on alternate bank (bank currently unused) by programming
|
||||
ChannelEn register.
|
||||
|
||||
(2) All the current configuration of Bus and active stream(s) are programmed
|
||||
into alternate bank (bank currently unused).
|
||||
|
||||
(3) Once all the values are programmed, Bus initiates switch to alternate
|
||||
bank where all new values programmed gets into effect and port(s) associated
|
||||
with current stream are disabled.
|
||||
|
||||
After all above operations are successful, stream state is set to
|
||||
``SDW_STREAM_DISABLED``.
|
||||
|
||||
Bus implements below API for DISABLED state which needs to be called once
|
||||
per stream. From ASoC DPCM framework, this stream state is linked to
|
||||
.trigger() stop operation.
|
||||
|
||||
.. code-block:: c
|
||||
int sdw_disable_stream(struct sdw_stream_runtime * stream);
|
||||
|
||||
|
||||
SDW_STREAM_DEPREPARED
|
||||
~~~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
De-prepare state of stream. Operations performed before entering in this
|
||||
state:
|
||||
|
||||
(1) All the port(s) of Master(s) and Slave(s) for current stream are
|
||||
de-prepared by programming PrepareCtrl register.
|
||||
|
||||
(2) The payload bandwidth of current stream is reduced from the total
|
||||
bandwidth requirement of bus and new parameters calculated and
|
||||
applied by performing bank switch etc.
|
||||
|
||||
After all above operations are successful, stream state is set to
|
||||
``SDW_STREAM_DEPREPARED``.
|
||||
|
||||
Bus implements below API for DEPREPARED state which needs to be called once
|
||||
per stream. From ASoC DPCM framework, this stream state is linked to
|
||||
.trigger() stop operation.
|
||||
|
||||
.. code-block:: c
|
||||
int sdw_deprepare_stream(struct sdw_stream_runtime * stream);
|
||||
|
||||
|
||||
SDW_STREAM_RELEASED
|
||||
~~~~~~~~~~~~~~~~~~~
|
||||
|
||||
Release state of stream. Operations performed before entering in this state:
|
||||
|
||||
(1) Release port resources for all Master(s) and Slave(s) port(s)
|
||||
associated with current stream.
|
||||
|
||||
(2) Release Master(s) and Slave(s) runtime resources associated with
|
||||
current stream.
|
||||
|
||||
(3) Release stream runtime resources associated with current stream.
|
||||
|
||||
After all above operations are successful, stream state is set to
|
||||
``SDW_STREAM_RELEASED``.
|
||||
|
||||
Bus implements below APIs for RELEASE state which needs to be called by
|
||||
all the Master(s) and Slave(s) associated with stream. From ASoC DPCM
|
||||
framework, this stream state is linked to .hw_free() operation.
|
||||
|
||||
.. code-block:: c
|
||||
int sdw_stream_remove_master(struct sdw_bus * bus,
|
||||
struct sdw_stream_runtime * stream);
|
||||
int sdw_stream_remove_slave(struct sdw_slave * slave,
|
||||
struct sdw_stream_runtime * stream);
|
||||
|
||||
|
||||
The .shutdown() ASoC DPCM operation calls below Bus API to release
|
||||
stream assigned as part of ALLOCATED state.
|
||||
|
||||
In .shutdown() the data structure maintaining stream state are freed up.
|
||||
|
||||
.. code-block:: c
|
||||
void sdw_release_stream(struct sdw_stream_runtime * stream);
|
||||
|
||||
Not Supported
|
||||
=============
|
||||
|
||||
1. A single port with multiple channels supported cannot be used between two
|
||||
streams or across stream. For example a port with 4 channels cannot be used
|
||||
to handle 2 independent stereo streams even though it's possible in theory
|
||||
in SoundWire.
|
||||
Loading…
Reference in New Issue
Block a user