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SubjectRe: [PATCH] ANDROID: sound: usb: Add vendor's hooking interface
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On 6/16/20 9:18 PM, JaeHun Jung wrote:
> In mobile, a co-processor is used when using USB audio
> to improve power consumption.
> hooking is required for sync-up when operating
> the co-processor. So register call-back function.
> The main operation of the call-back function is as follows:
> - Initialize the co-processor by transmitting data
> when initializing.
> - Change the co-processor setting value through
> the interface function.
> - Configure sampling rate
> - pcm open/close

Thank you for this patch. With the removal of the 3.5mm jack on a number
of platforms, and improvements to reduce power consumption on a variety
of hosts there's indeed a need to enhance sound/usb in the kernel.

>
> Bug: 156315379
>
> Change-Id: I32e1dd408e64aaef68ee06c480c4b4d4c95546dc
> Signed-off-by: JaeHun Jung <jh0801.jung@samsung.com>

You probably want to remove bug references and Change-Id if they are not
publicly visible

> @@ -891,6 +897,15 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
> struct usb_interface *iface;
> int ret;
>
> + if (usb_audio_ops && usb_audio_ops->vendor_set_pcmbuf) {
> + ret = usb_audio_ops->vendor_set_pcmbuf(subs->dev);
> +
> + if (ret < 0) {
> + dev_err(&subs->dev->dev, "pcm buf transfer failed\n");
> + return ret;
> + }
> + }
> +
> if (! subs->cur_audiofmt) {
> dev_err(&subs->dev->dev, "no format is specified!\n");
> return -ENXIO;
> @@ -924,6 +939,15 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
> if (ret < 0)
> goto unlock;
>
> + if (usb_audio_ops && usb_audio_ops->vendor_set_rate) {
> + subs->need_setup_ep = false;
> + usb_audio_ops->vendor_set_rate(
> + subs->cur_audiofmt->iface,
> + subs->cur_rate,
> + subs->cur_audiofmt->altsetting);
> + goto unlock;
> + }
> +
> ret = configure_endpoint(subs);
> if (ret < 0)
> goto unlock;
> @@ -1333,6 +1357,9 @@ static int snd_usb_pcm_open(struct snd_pcm_substream *substream)
> struct snd_usb_substream *subs = &as->substream[direction];
> int ret;
>
> + if (usb_audio_ops && usb_audio_ops->vendor_pcm_con)
> + usb_audio_ops->vendor_pcm_con(true, direction);
> +
> subs->interface = -1;
> subs->altset_idx = 0;
> runtime->hw = snd_usb_hardware;
> @@ -1361,12 +1388,18 @@ static int snd_usb_pcm_close(struct snd_pcm_substream *substream)
> struct snd_usb_substream *subs = &as->substream[direction];
> int ret;
>
> + if (usb_audio_ops && usb_audio_ops->vendor_pcm_con)
> + usb_audio_ops->vendor_pcm_con(false, direction);
> +

can you elaborate on the PCM streaming parts? if you allocate a buffer
for the co-processor to deal with PCM data, will you end-up copying data
from the existing ring buffers allocated with vmalloc() into your
coprocessor?

I was instead thinking of having a different 'mode' where the PCM
buffers are not allocated by sound/usb, but instead allocated by the
driver taking care of the low-power USB path, so that apps can directly
write into ring buffers that are handled by the coprocessor/offload unit.

Thanks
-Pierre

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