[PATCH rtw-next v2] wifi: rtw88: usb: Download the reserved page synchronously

[Bitterblue Smith <rtl8821cerfe2@gmail.com>]

From: Mohammed Afifi <i.mafifi17@gmail.com>

In AP mode the reserved page (which contains the beacon) is downloaded
to the chip by rtw_fw_write_data_rsvd_page(). That function writes the
data via rtw_hci_write_data_rsvd_page() and then immediately polls the
hardware BCN_VALID bit to confirm the firmware accepted the beacon.

On USB, rtw_usb_write_data_rsvd_page() ends up in rtw_usb_write_port(),
which submits the URB with usb_submit_urb() and returns as soon as the
transfer is queued. The completion callback only frees the skb. As a
result the BCN_VALID poll can run while the beacon is still in flight
on the bus, and the poll times out even though the download itself is
fine.

This shows up as:

  rtw_8822bu: error beacon valid
  rtw_8822bu: failed to download drv rsvd page

The failure is intermittent because the poll retries sometimes cover
the transfer time. It occurs in bursts when something triggers repeated
beacon updates, such as stations associating and disassociating.

Fix this by adding a synchronous bulk-out helper that waits for the URB
to complete, and using it for the reserved page download. Only the
reserved page / beacon path is made synchronous; the normal data TX
path is left untouched, so throughput is unaffected.

The reserved page download runs in process context under rtwdev->mutex,
so sleeping there is safe.

Closes: https://github.com/lwfinger/rtw88/issues/451
Signed-off-by: Mohammed Afifi <i.mafifi17@gmail.com>
Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
---
v2:
 - Fix compilation error in rtw_usb_write_data_rsvd_page().
---
 drivers/net/wireless/realtek/rtw88/usb.c | 91 +++++++++++++++++++++++-
 1 file changed, 90 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/realtek/rtw88/usb.c b/drivers/net/wireless/realtek/rtw88/usb.c
index c90802919473..d31297954f22 100644
--- a/drivers/net/wireless/realtek/rtw88/usb.c
+++ b/drivers/net/wireless/realtek/rtw88/usb.c
@@ -394,6 +394,71 @@ static int rtw_usb_write_port(struct rtw_dev *rtwdev, u8 qsel, struct sk_buff *s
 	return ret;
 }
 
+struct rtw_usb_write_data_sync_cb {
+	struct completion done;
+	int status;
+};
+
+static void rtw_usb_write_port_sync_complete(struct urb *urb)
+{
+	struct rtw_usb_write_data_sync_cb *cb = urb->context;
+
+	cb->status = urb->status;
+	complete(&cb->done);
+}
+
+/* Synchronous bulk-out that returns only after the data has actually been
+ * transferred to the device. Required for the reserved-page / beacon
+ * download: the caller polls the hardware BCN_VALID bit immediately after
+ * this returns, so the bytes must be on the chip by then. The normal async
+ * TX path races that poll, which shows up as intermittent
+ * "error beacon valid" / "failed to download drv rsvd page" in AP mode,
+ * more often on 5 GHz where the larger beacon takes longer to transfer.
+ */
+static int rtw_usb_write_port_sync(struct rtw_dev *rtwdev, u8 qsel,
+				   struct sk_buff *skb)
+{
+	struct rtw_usb *rtwusb = rtw_get_usb_priv(rtwdev);
+	struct usb_device *usbd = rtwusb->udev;
+	struct rtw_usb_write_data_sync_cb cb;
+	int ep = qsel_to_ep(rtwusb, qsel);
+	unsigned int pipe;
+	struct urb *urb;
+	int ret;
+
+	if (ep < 0)
+		return ep;
+
+	urb = usb_alloc_urb(0, GFP_KERNEL);
+	if (!urb)
+		return -ENOMEM;
+
+	init_completion(&cb.done);
+	cb.status = -EINPROGRESS;
+
+	pipe = usb_sndbulkpipe(usbd, rtwusb->out_ep[ep]);
+	usb_fill_bulk_urb(urb, usbd, pipe, skb->data, skb->len,
+			  rtw_usb_write_port_sync_complete, &cb);
+	urb->transfer_flags |= URB_ZERO_PACKET;
+
+	ret = usb_submit_urb(urb, GFP_KERNEL);
+	if (ret)
+		goto out;
+
+	/* 5 s matches the vendor driver's bulk-out timeout */
+	if (!wait_for_completion_timeout(&cb.done, msecs_to_jiffies(5000))) {
+		usb_kill_urb(urb);
+		ret = -ETIMEDOUT;
+	} else {
+		ret = cb.status;
+	}
+
+out:
+	usb_free_urb(urb);
+
+	return ret;
+}
+
 static bool rtw_usb_tx_agg_skb(struct rtw_usb *rtwusb, struct sk_buff_head *list)
 {
 	struct rtw_dev *rtwdev = rtwusb->rtwdev;
@@ -543,13 +608,37 @@ static int rtw_usb_write_data_rsvd_page(struct rtw_dev *rtwdev, u8 *buf,
 {
 	const struct rtw_chip_info *chip = rtwdev->chip;
 	struct rtw_tx_pkt_info pkt_info = {0};
+	struct sk_buff *skb;
+	int ret;
 
 	pkt_info.tx_pkt_size = size;
 	pkt_info.qsel = TX_DESC_QSEL_BEACON;
 	pkt_info.offset = chip->tx_pkt_desc_sz;
 	pkt_info.ls = true;
 
-	return rtw_usb_write_data(rtwdev, &pkt_info, buf);
+	skb = dev_alloc_skb(chip->tx_pkt_desc_sz + size);
+	if (!skb)
+		return -ENOMEM;
+
+	skb_reserve(skb, chip->tx_pkt_desc_sz);
+	skb_put_data(skb, buf, size);
+	skb_push(skb, chip->tx_pkt_desc_sz);
+	memset(skb->data, 0, chip->tx_pkt_desc_sz);
+	rtw_tx_fill_tx_desc(rtwdev, &pkt_info, skb);
+	rtw_tx_fill_txdesc_checksum(rtwdev, &pkt_info, skb->data);
+
+	/* Download the beacon/reserved page synchronously so that the caller's
+	 * subsequent BCN_VALID poll observes the completed transfer instead of
+	 * racing the async TX path.
+	 */
+	ret = rtw_usb_write_port_sync(rtwdev, pkt_info.qsel, skb);
+	if (ret)
+		rtw_err(rtwdev, "failed to download rsvd page over USB, ret=%d\n",
+			ret);
+
+	dev_kfree_skb_any(skb);
+
+	return ret;
 }
 
 static int rtw_usb_write_data_h2c(struct rtw_dev *rtwdev, u8 *buf, u32 size)
-- 
2.55.0