linux-kernel - [PATCH] media: uvcvideo: Support large SuperSpeedPlus isochronous endpoints

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Message-ID: <20250421095951.1e63824e@foxbook>
Date: Mon, 21 Apr 2025 09:59:51 +0200
From: Michal Pecio <michal.pecio@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, Hans de Goede
 <hdegoede@...hat.com>, Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org
Subject: [PATCH] media: uvcvideo: Support large SuperSpeedPlus isochronous
 endpoints

USB 3.1 increased maximum isochronous bandwidth to 96KB per interval,
too much for 16 bits and the SuperSpeed Endpoint Companion descriptor.
A new SuperSpeedPlus Isochronous Endpoint Companion descriptor was
introduced to encode such bandwidths, see spec sections 9.6.7, 9.6.8.

Support the descriptor with code based on xhci_get_max_esit_payload()
and widen all 'psize' variables to 32 bits. Subsequent calculations
are 32 bit already and not expected to overflow, so this change ought
to suffice for proper alt setting selection on USB 3.x Gen 2 devices.

Signed-off-by: Michal Pecio <michal.pecio@...il.com>
---

This change appears to be a strict necessity for supporting USB3 Gen2
isochronous devices meaningfully. Whether it's sufficient I don't know,
I don't have such HW. No regression seen on High Speed and SuperSpeed.

 drivers/media/usb/uvc/uvc_
 drivers/media/usb/uvc/uvc_driver.c |  2 +-
 drivers/media/usb/uvc/uvc_video.c  | 13 +++++++++----
 drivers/media/usb/uvc/uvcvideo.h   |  4 ++--
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 107e0fafd80f..60eaff81a8c0 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -536,7 +536,7 @@ static int uvc_parse_streaming(struct uvc_device *dev,
 	unsigned int nformats = 0, nframes = 0, nintervals = 0;
 	unsigned int size, i, n, p;
 	u32 *interval;
-	u16 psize;
+	u32 psize;
 	int ret = -EINVAL;
 
 	if (intf->cur_altsetting->desc.bInterfaceSubClass
diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index e3567aeb0007..591fbfcda2c1 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1898,13 +1898,18 @@ static void uvc_video_stop_transfer(struct uvc_streaming *stream,
 /*
  * Compute the maximum number of bytes per interval for an endpoint.
  */
-u16 uvc_endpoint_max_bpi(struct usb_device *dev, struct usb_host_endpoint *ep)
+u32 uvc_endpoint_max_bpi(struct usb_device *dev, struct usb_host_endpoint *ep)
 {
-	u16 psize;
+	u32 psize;
 
 	switch (dev->speed) {
-	case USB_SPEED_SUPER:
 	case USB_SPEED_SUPER_PLUS:
+		/* check for the SS+ Isoc EP Companion descriptor */
+		if (USB_SS_SSP_ISOC_COMP(ep->ss_ep_comp.bmAttributes))
+			return le32_to_cpu(ep->ssp_isoc_ep_comp.dwBytesPerInterval);
+		fallthrough;
+	case USB_SPEED_SUPER:
+		/* use the SS EP Companion descriptor */
 		return le16_to_cpu(ep->ss_ep_comp.wBytesPerInterval);
 	default:
 		psize = usb_endpoint_maxp(&ep->desc);
@@ -1923,7 +1928,7 @@ static int uvc_init_video_isoc(struct uvc_streaming *stream,
 	struct urb *urb;
 	struct uvc_urb *uvc_urb;
 	unsigned int npackets, i;
-	u16 psize;
+	u32 psize;
 	u32 size;
 
 	psize = uvc_endpoint_max_bpi(stream->dev->udev, ep);
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index b4ee701835fc..b0a5ddff6dda 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -450,7 +450,7 @@ struct uvc_streaming {
 
 	struct usb_interface *intf;
 	int intfnum;
-	u16 maxpsize;
+	u32 maxpsize;
 
 	struct uvc_streaming_header header;
 	enum v4l2_buf_type type;
@@ -813,7 +813,7 @@ void uvc_ctrl_cleanup_fh(struct uvc_fh *handle);
 /* Utility functions */
 struct usb_host_endpoint *uvc_find_endpoint(struct usb_host_interface *alts,
 					    u8 epaddr);
-u16 uvc_endpoint_max_bpi(struct usb_device *dev, struct usb_host_endpoint *ep);
+u32 uvc_endpoint_max_bpi(struct usb_device *dev, struct usb_host_endpoint *ep);
 
 /* Quirks support */
 void uvc_video_decode_isight(struct uvc_urb *uvc_urb,
-- 
2.48.1