| Message ID | 20240507195116.9464-23-quic_wcheng@quicinc.com |
|---|---|
| State | New |
| Headers | show |
| Series | Introduce QC USB SND audio offloading support | expand |
> If a PCM device is already in use, the check will return an error to > userspace notifying that the stream is currently busy. This ensures that > only one path is using the USB substream. What was the point of having a "USB Mixer" then?
Hi Pierre, On 5/7/2024 2:20 PM, Pierre-Louis Bossart wrote: > >> If a PCM device is already in use, the check will return an error to >> userspace notifying that the stream is currently busy. This ensures that >> only one path is using the USB substream. > > What was the point of having a "USB Mixer" then? The USB mixer is intended to enable/route the USB offloading path to the audio DSP, and is for controlling the ASoC specific entities. This change is needed to resolve any contention between the USB SND PCM device (non offload path) and the ASoC USB BE DAI (offload path). Thanks Wesley Cheng
On 5/8/24 18:40, Wesley Cheng wrote: > Hi Pierre, > > On 5/7/2024 2:20 PM, Pierre-Louis Bossart wrote: >> >>> If a PCM device is already in use, the check will return an error to >>> userspace notifying that the stream is currently busy. This ensures >>> that >>> only one path is using the USB substream. >> >> What was the point of having a "USB Mixer" then? > > The USB mixer is intended to enable/route the USB offloading path to the > audio DSP, and is for controlling the ASoC specific entities. This > change is needed to resolve any contention between the USB SND PCM > device (non offload path) and the ASoC USB BE DAI (offload path). Not following, sorry. Is the "USB Mixer" some sort of hardware entity related to USB offload or just a pure DAPM processing widget handling volume and actual mixing between streams? I was trying to get clarity on whether there can be multiple streams mixed before going to the USB endpoint. The commit message "only one path is using the USB substream" is ambiguous, not sure if you are referring to mutual exclusion between offloaded and non-offloaded paths, or number of streams when offloaded is supported. Different concepts/levels.
Hi Pierre, On 5/9/2024 6:01 AM, Pierre-Louis Bossart wrote: > > > On 5/8/24 18:40, Wesley Cheng wrote: >> Hi Pierre, >> >> On 5/7/2024 2:20 PM, Pierre-Louis Bossart wrote: >>> >>>> If a PCM device is already in use, the check will return an error to >>>> userspace notifying that the stream is currently busy. This ensures >>>> that >>>> only one path is using the USB substream. >>> >>> What was the point of having a "USB Mixer" then? >> >> The USB mixer is intended to enable/route the USB offloading path to the >> audio DSP, and is for controlling the ASoC specific entities. This >> change is needed to resolve any contention between the USB SND PCM >> device (non offload path) and the ASoC USB BE DAI (offload path). > > Not following, sorry. Is the "USB Mixer" some sort of hardware entity > related to USB offload or just a pure DAPM processing widget handling > volume and actual mixing between streams? > It controls which Multimedia (ASM) stream can be routed to the USB BE DAI. > I was trying to get clarity on whether there can be multiple streams > mixed before going to the USB endpoint. The commit message "only one > path is using the USB substream" is ambiguous, not sure if you are > referring to mutual exclusion between offloaded and non-offloaded paths, > or number of streams when offloaded is supported. Different concepts/levels. Ideally we shouldn't. Only one ASM stream should be allowed to open the USB AFE port at a time. Thanks Wesley Cheng
diff --git a/sound/usb/card.h b/sound/usb/card.h index d66cc0b139af..3c900e5afbce 100644 --- a/sound/usb/card.h +++ b/sound/usb/card.h @@ -165,6 +165,7 @@ struct snd_usb_substream { unsigned int pkt_offset_adj; /* Bytes to drop from beginning of packets (for non-compliant devices) */ unsigned int stream_offset_adj; /* Bytes to drop from beginning of stream (for non-compliant devices) */ + unsigned int opened:1; /* pcm device opened */ unsigned int running: 1; /* running status */ unsigned int period_elapsed_pending; /* delay period handling */ diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c index 3adb09ce1702..3e6d33de6ce6 100644 --- a/sound/usb/pcm.c +++ b/sound/usb/pcm.c @@ -1241,8 +1241,17 @@ static int snd_usb_pcm_open(struct snd_pcm_substream *substream) struct snd_usb_stream *as = snd_pcm_substream_chip(substream); struct snd_pcm_runtime *runtime = substream->runtime; struct snd_usb_substream *subs = &as->substream[direction]; + struct snd_usb_audio *chip = subs->stream->chip; int ret; + mutex_lock(&chip->mutex); + if (subs->opened) { + mutex_unlock(&chip->mutex); + return -EBUSY; + } + subs->opened = 1; + mutex_unlock(&chip->mutex); + runtime->hw = snd_usb_hardware; /* need an explicit sync to catch applptr update in low-latency mode */ if (direction == SNDRV_PCM_STREAM_PLAYBACK && @@ -1259,13 +1268,23 @@ static int snd_usb_pcm_open(struct snd_pcm_substream *substream) ret = setup_hw_info(runtime, subs); if (ret < 0) - return ret; + goto err_open; ret = snd_usb_autoresume(subs->stream->chip); if (ret < 0) - return ret; + goto err_open; ret = snd_media_stream_init(subs, as->pcm, direction); if (ret < 0) - snd_usb_autosuspend(subs->stream->chip); + goto err_resume; + + return 0; + +err_resume: + snd_usb_autosuspend(subs->stream->chip); +err_open: + mutex_lock(&chip->mutex); + subs->opened = 0; + mutex_unlock(&chip->mutex); + return ret; } @@ -1274,6 +1293,7 @@ static int snd_usb_pcm_close(struct snd_pcm_substream *substream) int direction = substream->stream; struct snd_usb_stream *as = snd_pcm_substream_chip(substream); struct snd_usb_substream *subs = &as->substream[direction]; + struct snd_usb_audio *chip = subs->stream->chip; int ret; snd_media_stop_pipeline(subs); @@ -1287,6 +1307,9 @@ static int snd_usb_pcm_close(struct snd_pcm_substream *substream) subs->pcm_substream = NULL; snd_usb_autosuspend(subs->stream->chip); + mutex_lock(&chip->mutex); + subs->opened = 0; + mutex_unlock(&chip->mutex); return 0; }
With USB audio offloading, an audio session is started from the ASoC platform sound card and PCM devices. Likewise, the USB SND path is still readily available for use, in case the non-offload path is desired. In order to prevent the two entities from attempting to use the USB bus, introduce a flag that determines when either paths are in use. If a PCM device is already in use, the check will return an error to userspace notifying that the stream is currently busy. This ensures that only one path is using the USB substream. Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com> --- sound/usb/card.h | 1 + sound/usb/pcm.c | 29 ++++++++++++++++++++++++++--- 2 files changed, 27 insertions(+), 3 deletions(-)