[PATCH 2/2] ALSA: usb-audio: qcom: request page-aligned xHCI ring buffers

[Wesley Cheng <wesley.cheng@oss.qualcomm.com>]

Now that xhci sideband supports requesting a specific ring alignment,
ask for PAGE_SIZE alignment when adding the data/sync endpoints to the
sideband and when creating the interrupter's event ring, so the
buffers reported to the ADSP over QMI always start at a page boundary
and span a full page.

xhci_sideband_add_endpoint() must run before the endpoint's transfer
ring is first allocated (i.e. before snd_usb_endpoint_prepare()
triggers xhci_endpoint_init()) for the alignment request to apply to
that first allocation. Move the xhci_sideband_add_endpoint() calls out
of uaudio_endpoint_setup() and into enable_audio_stream(), before
snd_usb_endpoint_prepare() is called for the data and sync endpoints,
and unwind them on the new error paths.

At that point in the setup sequence dev->ep_in[]/ep_out[] are not yet
populated, since the endpoint's altsetting has not been activated, so
usb_pipe_endpoint() cannot be used to find the usb_host_endpoint. Add
uaudio_find_host_endpoint(), which resolves it directly from the
interface's altsetting descriptor table instead.

Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Wesley Cheng <wesley.cheng@oss.qualcomm.com>
---
 sound/usb/qcom/qc_audio_offload.c | 96 +++++++++++++++++++++++++++++++++------
 1 file changed, 82 insertions(+), 14 deletions(-)

diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
index e4bfd43a2488..87e016104c3d 100644
--- a/sound/usb/qcom/qc_audio_offload.c
+++ b/sound/usb/qcom/qc_audio_offload.c
@@ -941,6 +941,45 @@ static void uaudio_dev_release(struct kref *kref)
 	wake_up(&dev->disconnect_wq);
 }
 
+/**
+ * uaudio_find_host_endpoint() - look up usb_host_endpoint for a snd_usb_endpoint
+ * @subs: usb substream owning the target snd_usb_endpoint
+ * @endpoint: sync or data snd_usb_endpoint to resolve
+ *
+ * usb_pipe_endpoint() resolves via dev->ep_in[]/ep_out[], which are only
+ * populated once usb_set_interface() has activated the endpoint's altsetting
+ * (i.e. after snd_usb_endpoint_prepare() has run for it). Looking that up
+ * beforehand returns NULL.
+ *
+ * Instead, look the endpoint up directly in the interface's altsetting
+ * descriptor table, which is populated once at enumeration time and stays
+ * valid regardless of which altsetting is currently active.
+ *
+ * Return: matching usb_host_endpoint, or NULL if not found.
+ */
+static struct usb_host_endpoint *
+uaudio_find_host_endpoint(struct snd_usb_substream *subs,
+			  struct snd_usb_endpoint *endpoint)
+{
+	struct usb_host_interface *alt;
+	struct usb_interface *iface;
+	int i;
+
+	iface = usb_ifnum_to_if(subs->dev, endpoint->iface);
+	if (!iface)
+		return NULL;
+
+	alt = usb_altnum_to_altsetting(iface, endpoint->altsetting);
+	if (!alt)
+		return NULL;
+
+	for (i = 0; i < alt->desc.bNumEndpoints; i++)
+		if (alt->endpoint[i].desc.bEndpointAddress == endpoint->ep_num)
+			return &alt->endpoint[i];
+
+	return NULL;
+}
+
 /**
  * enable_audio_stream() - enable usb snd endpoints
  * @subs: usb substream
@@ -958,8 +997,9 @@ static void uaudio_dev_release(struct kref *kref)
 static int enable_audio_stream(struct snd_usb_substream *subs,
 			       snd_pcm_format_t pcm_format,
 			       unsigned int channels, unsigned int cur_rate,
-			       int datainterval)
+			       int datainterval, unsigned int card_num)
 {
+	struct usb_host_endpoint *data_ep = NULL, *sync_ep = NULL;
 	struct snd_pcm_hw_params params;
 	struct snd_usb_audio *chip;
 	struct snd_interval *i;
@@ -997,17 +1037,47 @@ static int enable_audio_stream(struct snd_usb_substream *subs,
 			goto detach_ep;
 		}
 
+		data_ep = uaudio_find_host_endpoint(subs, subs->data_endpoint);
+		if (!data_ep) {
+			dev_err(&subs->dev->dev, "data ep # %d not found\n",
+				subs->data_endpoint->ep_num);
+			ret = -ENODEV;
+			goto detach_ep;
+		}
+
+		ret = xhci_sideband_add_endpoint(uadev[card_num].sb, data_ep, PAGE_SIZE);
+		if (ret < 0) {
+			dev_err(&subs->dev->dev,
+				"failed to add data ep to sec intr: %d\n", ret);
+			goto detach_ep;
+		}
+
 		if (subs->sync_endpoint) {
+			sync_ep = uaudio_find_host_endpoint(subs, subs->sync_endpoint);
+			if (!sync_ep) {
+				dev_err(&subs->dev->dev, "sync ep # %d not found\n",
+					subs->sync_endpoint->ep_num);
+				ret = -ENODEV;
+				goto remove_data_ep;
+			}
+
+			ret = xhci_sideband_add_endpoint(uadev[card_num].sb, sync_ep, PAGE_SIZE);
+			if (ret < 0) {
+				dev_err(&subs->dev->dev,
+					"failed to add sync ep to sec intr: %d\n", ret);
+				goto remove_data_ep;
+			}
+
 			ret = snd_usb_endpoint_prepare(chip, subs->sync_endpoint);
 			if (ret < 0)
-				goto detach_ep;
+				goto remove_sync_ep;
 		}
 
 		ret = snd_usb_endpoint_prepare(chip, subs->data_endpoint);
 		if (ret < 0)
-			goto detach_ep;
+			goto remove_sync_ep;
 
-		dev_dbg(uaudio_qdev->data->dev,
+		dev_dbg(&subs->dev->dev,
 			"selected %s iface:%d altsetting:%d datainterval:%dus\n",
 			subs->direction ? "capture" : "playback",
 			subs->cur_audiofmt->iface, subs->cur_audiofmt->altsetting,
@@ -1019,6 +1089,11 @@ static int enable_audio_stream(struct snd_usb_substream *subs,
 
 	return 0;
 
+remove_sync_ep:
+	if (sync_ep)
+		xhci_sideband_remove_endpoint(uadev[card_num].sb, sync_ep);
+remove_data_ep:
+	xhci_sideband_remove_endpoint(uadev[card_num].sb, data_ep);
 detach_ep:
 	snd_usb_hw_free(subs);
 
@@ -1140,14 +1215,6 @@ uaudio_endpoint_setup(struct snd_usb_substream *subs,
 
 	memcpy(ep_desc, &ep->desc, sizeof(ep->desc));
 
-	ret = xhci_sideband_add_endpoint(uadev[card_num].sb, ep);
-	if (ret < 0) {
-		dev_err(&subs->dev->dev,
-			"failed to add data ep to sec intr: %d\n", ret);
-		ret = -ENODEV;
-		goto exit;
-	}
-
 	sgt = xhci_sideband_get_endpoint_buffer(uadev[card_num].sb, ep);
 	if (!sgt) {
 		dev_err(&subs->dev->dev,
@@ -1212,7 +1279,8 @@ static int uaudio_event_ring_setup(struct snd_usb_substream *subs,
 
 	/* event ring */
 	ret = xhci_sideband_create_interrupter(uadev[card_num].sb, 1, false,
-					       0, uaudio_qdev->data->intr_num);
+					       0, uaudio_qdev->data->intr_num,
+					       PAGE_SIZE);
 	if (ret < 0) {
 		dev_err(&subs->dev->dev, "failed to fetch interrupter\n");
 		goto put_offload;
@@ -1637,7 +1705,7 @@ static void handle_uaudio_stream_req(struct qmi_handle *handle,
 		ret = enable_audio_stream(subs,
 					  map_pcm_format(req_msg->audio_format),
 					  req_msg->number_of_ch, req_msg->bit_rate,
-					  datainterval);
+					  datainterval, pcm_card_num);
 
 		if (!ret)
 			ret = prepare_qmi_response(subs, req_msg, &resp,

-- 
2.34.1