[PATCH v6 1/2] media: uvcvideo: add UVC_QUIRK_CTRL_THROTTLE for fragile USB firmware

[JP Hein <jp@jphein.com>]

Some UVC devices have firmware that locks up under sustained rapid
USB control transfers, crashing the xHCI host controller and taking
all USB devices on the bus with it.

The Razer Kiyo Pro (1532:0e05) is the first known example: approximately
25 rapid consecutive control transfers cause the firmware to stall an
endpoint. The kernel's standard UVC error recovery (GET_CUR on
UVC_VC_REQUEST_ERROR_CODE_CONTROL) then sends a second transfer to the
already-stalling device, amplifying the failure into complete firmware
lockup and xHCI controller death.

Add UVC_QUIRK_CTRL_THROTTLE which:
  - Rate-limits all USB control transfers to 50ms intervals in
    __uvc_query_ctrl(), the lowest-level UVC control transfer function,
    ensuring all callers are throttled including uvc_set_video_ctrl()
    which bypasses uvc_query_ctrl()
  - Skips the error-code query after EPIPE to avoid amplifying stalls

The 50ms interval was determined experimentally: the device is stable
at this rate under sustained operation, while shorter intervals
eventually trigger the firmware bug.

Signed-off-by: JP Hein <jp@jphein.com>
---
 drivers/media/usb/uvc/uvc_video.c | 30 ++++++++++++++++++++++++++++++
 drivers/media/usb/uvc/uvcvideo.h  |  3 +++
 2 files changed, 33 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index a5013a7..cee93ac 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -36,6 +36,26 @@ static int __uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
 	u8 type = USB_TYPE_CLASS | USB_RECIP_INTERFACE;
 	unsigned int pipe;
 
+	/*
+	 * Rate-limit control transfers for devices with fragile firmware.
+	 * The Razer Kiyo Pro locks up under sustained rapid control
+	 * transfers (hundreds without delay), crashing the xHCI controller.
+	 * Throttle in this low-level function to cover all callers,
+	 * including uvc_set_video_ctrl() which bypasses uvc_query_ctrl().
+	 */
+	if (dev->quirks & UVC_QUIRK_CTRL_THROTTLE) {
+		unsigned long min_interval = msecs_to_jiffies(50);
+
+		if (dev->last_ctrl_jiffies &&
+		    time_before(jiffies,
+				dev->last_ctrl_jiffies + min_interval)) {
+			unsigned long wait = dev->last_ctrl_jiffies +
+					     min_interval - jiffies;
+			msleep(jiffies_to_msecs(wait));
+		}
+		dev->last_ctrl_jiffies = jiffies;
+	}
+
 	pipe = (query & 0x80) ? usb_rcvctrlpipe(dev->udev, 0)
 			      : usb_sndctrlpipe(dev->udev, 0);
 	type |= (query & 0x80) ? USB_DIR_IN : USB_DIR_OUT;
@@ -108,6 +128,16 @@ int uvc_query_ctrl(struct uvc_device *dev, u8 query, u8 unit,
 		return ret < 0 ? ret : -EPIPE;
 	}
 
+	/*
+	 * Skip the error code query for devices that crash under load.
+	 * The standard error-code query (GET_CUR on
+	 * UVC_VC_REQUEST_ERROR_CODE_CONTROL) sends a second USB transfer to
+	 * a device that is already stalling, which can amplify the failure
+	 * into a full firmware lockup and xHCI controller death.
+	 */
+	if (dev->quirks & UVC_QUIRK_CTRL_THROTTLE)
+		return -EPIPE;
+
 	/* Reuse data[0] to request the error code. */
 	tmp = *(u8 *)data;
 
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index 757254f..31f2af5 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -78,6 +78,7 @@
 #define UVC_QUIRK_INVALID_DEVICE_SOF	0x00010000
 #define UVC_QUIRK_MJPEG_NO_EOF		0x00020000
 #define UVC_QUIRK_MSXU_META		0x00040000
+#define UVC_QUIRK_CTRL_THROTTLE		0x00080000
 
 /* Format flags */
 #define UVC_FMT_FLAG_COMPRESSED		0x00000001
@@ -583,6 +584,8 @@ struct uvc_device {
 	struct usb_interface *intf;
 	unsigned long warnings;
 	u32 quirks;
+	/* UVC control transfer throttling (UVC_QUIRK_CTRL_THROTTLE) */
+	unsigned long last_ctrl_jiffies;
 	int intfnum;
 	char name[32];
 
-- 
2.43.0