linux-kernel - Re: [PATCH v18 20/41] ALSA: usb-audio: qcom: Introduce QC USB SND offloading support

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Date: Wed, 13 Mar 2024 16:03:03 +0800
From: Albert Wang <albertccwang@...gle.com>
To: Wesley Cheng <quic_wcheng@...cinc.com>
Cc: srinivas.kandagatla@...aro.org, mathias.nyman@...el.com, perex@...ex.cz, 
	conor+dt@...nel.org, corbet@....net, lgirdwood@...il.com, 
	andersson@...nel.org, krzysztof.kozlowski+dt@...aro.org, 
	gregkh@...uxfoundation.org, Thinh.Nguyen@...opsys.com, broonie@...nel.org, 
	bgoswami@...cinc.com, tiwai@...e.com, robh+dt@...nel.org, 
	konrad.dybcio@...aro.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-sound@...r.kernel.org, 
	linux-usb@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-doc@...r.kernel.org, alsa-devel@...a-project.org
Subject: Re: [PATCH v18 20/41] ALSA: usb-audio: qcom: Introduce QC USB SND
 offloading support

+/**
+ * qc_usb_audio_offload_suspend() - USB offload PM suspend handler
+ * @intf: USB interface
+ * @message: suspend type
+ *
+ * PM suspend handler to ensure that the USB offloading driver is able to stop
+ * any pending traffic, so that the bus can be suspended.
+ *
+ */
+static void qc_usb_audio_offload_suspend(struct usb_interface *intf,
+                                               pm_message_t message)
+{
+       struct qmi_uaudio_stream_ind_msg_v01 disconnect_ind = {0};
+       struct snd_usb_audio *chip = usb_get_intfdata(intf);
+       struct uaudio_qmi_svc *svc = uaudio_svc;
+       struct uaudio_dev *dev;
+       int card_num;
+       int ret;
+
+       if (!chip)
+               return;
+
+       card_num = chip->card->number;
+       if (card_num >= SNDRV_CARDS)
+               return;
+
+
+       mutex_lock(&chip->mutex);
+       dev = &uadev[card_num];
+
+       if (atomic_read(&dev->in_use)) {
+               mutex_unlock(&chip->mutex);
+               dev_dbg(uaudio_qdev->data->dev, "sending qmi
indication suspend\n");
+               disconnect_ind.dev_event = USB_QMI_DEV_DISCONNECT_V01;
+               disconnect_ind.slot_id = dev->udev->slot_id;
+               disconnect_ind.controller_num = dev->usb_core_id;
+               disconnect_ind.controller_num_valid = 1;
+               ret = qmi_send_indication(svc->uaudio_svc_hdl, &svc->client_sq,
+                               QMI_UAUDIO_STREAM_IND_V01,
+                               QMI_UAUDIO_STREAM_IND_MSG_V01_MAX_MSG_LEN,
+                               qmi_uaudio_stream_ind_msg_v01_ei,
+                               &disconnect_ind);
+               if (ret < 0)
+                       dev_err(uaudio_qdev->data->dev,
+                               "qmi send failed with err: %d\n", ret);
+
+               ret = wait_event_interruptible_timeout(dev->disconnect_wq,
+                               !atomic_read(&dev->in_use),
+                               msecs_to_jiffies(DEV_RELEASE_WAIT_TIMEOUT));
+               if (!ret) {
+                       dev_err(uaudio_qdev->data->dev,
+                               "timeout while waiting for dev_release\n");
+                       atomic_set(&dev->in_use, 0);
+               } else if (ret < 0) {
+                       dev_err(uaudio_qdev->data->dev,
+                               "failed with ret %d\n", ret);
+                               atomic_set(&dev->in_use, 0);
+               }
+               mutex_lock(&chip->mutex);
+       }
+       mutex_unlock(&chip->mutex);
+}
+

Hi Wesley,

The suspend function `qc_usb_audio_offload_suspend()` looks to stop
the traffic on the bus, so that the bus can be suspended. That allows
the application processor(AP) to enter suspend. There is a subtle
difference with our feature, which is to allow AP suspend with the
Host and USB controller active to continue the audio offloading. We
call this feature `allow AP suspend in playback`. So, I have some
points to clarify with you:
1. Will the suspend flow `usb_audio_suspend() -->
platform_ops->suspend_cb() --> qc_usb_audio_offload_suspend()` be
called when offloading is active?
2. As my understanding, the suspend function is to allow AP suspend
when the offloading is IDLE, but it won't allow AP suspend when in
playback or capture. Please correct me if anything is wrong.
3. We would like to integrate the `allow AP suspend in playback`
feature with your framework to become one upstream offload solution.
Here is the patch:
https://patchwork.kernel.org/project/linux-pm/patch/20240223143833.1509961-1-guanyulin@google.com/
.

Thanks,
Albert