On 5/27/2024 9:11 AM, Jaroslav Kysela wrote:
There is a requirement to expose the audio hardware that accelerates various
tasks for user space such as sample rate converters, compressed
stream decoders, etc.
This is description for the API extension for the compress ALSA API which
is able to handle "tasks" that are not bound to real-time operations
and allows for the serialization of operations.
For details, refer to "compress-passthrough.rst" document.
Note: This code is RFC (not tested, just to clearify the API requirements).
My goal is to add a test (loopback) driver and add a support to tinycompress
library in the next step.
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Shengjiu Wang <shengjiu.wang@xxxxxxxxx>
Cc: Nicolas Dufresne <nicolas@xxxxxxxxxxxx>
Cc: Amadeusz Sławiński <amadeuszx.slawinski@xxxxxxxxxxxxxxx>
Cc: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
Cc: Vinod Koul <vkoul@xxxxxxxxxx>
Signed-off-by: Jaroslav Kysela <perex@xxxxxxxx>
---
Seems mostly ok to me, some nitpicks below.
.../sound/designs/compress-passthrough.rst | 125 +++++++
include/sound/compress_driver.h | 32 ++
include/uapi/sound/compress_offload.h | 44 ++-
sound/core/Kconfig | 4 +
sound/core/compress_offload.c | 314 +++++++++++++++++-
5 files changed, 511 insertions(+), 8 deletions(-)
create mode 100644 Documentation/sound/designs/compress-passthrough.rst
diff --git a/Documentation/sound/designs/compress-passthrough.rst b/Documentation/sound/designs/compress-passthrough.rst
new file mode 100644
index 000000000000..bb5a0ae5c496
--- /dev/null
+++ b/Documentation/sound/designs/compress-passthrough.rst
@@ -0,0 +1,125 @@
+=================================
+ALSA Co-processor Passthrough API
+=================================
+
+Jaroslav Kysela <perex@xxxxxxxx>
+
+
+Overview
+========
+
+There is a requirement to expose the audio hardware that accelerates various
+tasks for user space such as sample rate converters, compressed
+stream decoders, etc.
+
+This is description for the API extension for the compress ALSA API which
+is able to handle "tasks" that are not bound to real-time operations
+and allows for the serialization of operations.
+
+Requirements
+============
+
+The main requirements are:
+
+- serialization of multiple tasks for user space to allow multiple
+ operations without user space intervention
+
+- separate buffers (input + output) for each operation
+
+- expose buffers using mmap to user space
+
+- signal user space when the task is finished (standard poll mechanism)
+
+Design
+======
+
+A new direction SND_COMPRESS_PASSTHROUGH is introduced to identify
+the passthrough API.
+
+The API extension shares device enumeration and parameters handling from
+the main compressed API. All other realtime streaming ioctls are deactivated
+and a new set of task related ioctls are introduced. The standard
+read/write/mmap I/O operations are not supported in the passtrough device.
passthrough
+
+Device ("stream") state handling is reduced to OPEN/SETUP. All other
+states are not available for the passthrough mode.
+
+Data I/O mechanism is using standard dma-buf interface with all advantages
+like mmap, standard I/O, buffer sharing etc. One buffer is used for the
+input data and second (separate) buffer is used for the ouput data. Each task
output
+have separate I/O buffers.
+
+For the buffering parameters, the fragments means a limit of allocated tasks
+for given device. The fragment_size limits the input buffer size for the given
+device. The output buffer size is determined by the driver (may be different
+from the input buffer size).
+
+State Machine
+=============
+
+The passtrough audio stream state machine is described below :
passthrough
+
+ +----------+
+ | |
+ | OPEN |
+ | |
+ +----------+
+ |
+ |
+ | compr_set_params()
+ |
+ v
+ all passthrough task ops +----------+
+ +------------------------------------| |
+ | | SETUP |
+ | |
+ | +----------+
+ | |
+ +------------------------------------------+
+
+
+Passthrough operations (ioctls)
+===============================
+
+CREATE
+------
+Creates a set of input/output buffers. The input buffer size is
+fragment_size. Allocates unique seqno.
+
+The hardware drivers allocate internal 'struct dma_buf' for both input and
+output buffers (using 'dma_buf_export()' function). The anonymous
+file descriptors for those buffers are passed to user space.
+
+FREE
+----
+Free a set of input/output buffers. If an task is active, the stop
_a_ task?
+
+static int snd_compr_task_start(struct snd_compr_stream *stream, struct snd_compr_task *utask)
+{
+ struct snd_compr_task_runtime *task;
+ int retval;
+
+ if (utask->origin_seqno > 0) {
+ task = snd_compr_find_task(stream, utask->seqno);
+ retval = snd_compr_task_start_prepare(task, utask);
+ if (retval < 0)
+ return retval;
+ task->seqno = utask->seqno = snd_compr_seqno_next(stream);
+ utask->origin_seqno = 0;
+ list_move_tail(&task->list, &stream->runtime->tasks);
+ } else {
+ task = snd_compr_find_task(stream, utask->seqno);
+ if (task && task->finished)
+ return -EBUSY;
+ retval = snd_compr_task_start_prepare(task, utask);
+ if (retval < 0)
+ return retval;
+ }
+ retval = stream->ops->task_start(stream, task);
Should probably check somewhere that ops are set properly, or is it this
way because they all considered mandatory?
+
+static int snd_compr_task_status(struct snd_compr_stream *stream,
+ struct snd_compr_task_status *status)
+{
+ struct snd_compr_task_runtime *task;
+
+ task = snd_compr_find_task(stream, status->seqno);
+ if (task == NULL)
+ return -EINVAL;
+ status->output_size = task->output_size;
+ status->active = task->active ? 1 : 0;
+ status->finished = task->finished ? 1 : 0;
Not sure, but access to ->active and ->finished, feels to me like
something that may require locking.
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