USB: core: Add eUSB2 descriptor and parsing in USB core

Add support for the 'eUSB2 Isochronous Endpoint Companion Descriptor'
introduced in the recent USB 2.0 specification 'USB 2.0 Double Isochronous
IN Bandwidth' ECN.

It allows embedded USB2 (eUSB2) devices to report and use higher bandwidths
for isochronous IN transfers in order to support higher camera resolutions
on the lid of laptops and tablets with minimal change to the USB2 protocol.

The motivation for expanding USB 2.0 is further clarified in an additional
Embedded USB2 version 2.0 (eUSB2v2) supplement to the USB 2.0
specification. It points out this is optimized for performance, power and
cost by using the USB 2.0 low-voltage, power efficient PHY and half-duplex
link for the asymmetric camera bandwidth needs, avoiding the costly and
complex full-duplex USB 3.x symmetric link and gigabit receivers.

eUSB2 devices that support the higher isochronous IN bandwidth and the new
descriptor can be identified by their device descriptor bcdUSB value of
0x0220

Co-developed-by: Amardeep Rai <amardeep.rai@intel.com>
Signed-off-by: Amardeep Rai <amardeep.rai@intel.com>
Signed-off-by: Kannappan R <r.kannappan@intel.com>
Co-developed-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20250220141339.1939448-1-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 46 insertions, 5 deletions

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index f7bf8d1de3ad..13bd4ec4ea5f 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -64,6 +64,37 @@ static void usb_parse_ssp_isoc_endpoint_companion(struct device *ddev,
 	memcpy(&ep->ssp_isoc_ep_comp, desc, USB_DT_SSP_ISOC_EP_COMP_SIZE);
 }
 
+static void usb_parse_eusb2_isoc_endpoint_companion(struct device *ddev,
+		int cfgno, int inum, int asnum, struct usb_host_endpoint *ep,
+		unsigned char *buffer, int size)
+{
+	struct usb_eusb2_isoc_ep_comp_descriptor *desc;
+	struct usb_descriptor_header *h;
+
+	/*
+	 * eUSB2 isochronous endpoint companion descriptor for this endpoint
+	 * shall be declared before the next endpoint or interface descriptor
+	 */
+	while (size >= USB_DT_EUSB2_ISOC_EP_COMP_SIZE) {
+		h = (struct usb_descriptor_header *)buffer;
+
+		if (h->bDescriptorType == USB_DT_EUSB2_ISOC_ENDPOINT_COMP) {
+			desc = (struct usb_eusb2_isoc_ep_comp_descriptor *)buffer;
+			ep->eusb2_isoc_ep_comp = *desc;
+			return;
+		}
+		if (h->bDescriptorType == USB_DT_ENDPOINT ||
+		    h->bDescriptorType == USB_DT_INTERFACE)
+			break;
+
+		buffer += h->bLength;
+		size -= h->bLength;
+	}
+
+	dev_notice(ddev, "No eUSB2 isoc ep %d companion for config %d interface %d altsetting %d\n",
+		   ep->desc.bEndpointAddress, cfgno, inum, asnum);
+}
+
 static void usb_parse_ss_endpoint_companion(struct device *ddev, int cfgno,
 		int inum, int asnum, struct usb_host_endpoint *ep,
 		unsigned char *buffer, int size)
@@ -258,8 +289,10 @@ static int usb_parse_endpoint(struct device *ddev, int cfgno,
 	int n, i, j, retval;
 	unsigned int maxp;
 	const unsigned short *maxpacket_maxes;
+	u16 bcdUSB;
 
 	d = (struct usb_endpoint_descriptor *) buffer;
+	bcdUSB = le16_to_cpu(udev->descriptor.bcdUSB);
 	buffer += d->bLength;
 	size -= d->bLength;
 
@@ -409,15 +442,17 @@ static int usb_parse_endpoint(struct device *ddev, int cfgno,
 
 	/*
 	 * Validate the wMaxPacketSize field.
-	 * Some devices have isochronous endpoints in altsetting 0;
-	 * the USB-2 spec requires such endpoints to have wMaxPacketSize = 0
-	 * (see the end of section 5.6.3), so don't warn about them.
+	 * eUSB2 devices (see USB 2.0 Double Isochronous IN ECN 9.6.6 Endpoint)
+	 * and devices with isochronous endpoints in altsetting 0 (see USB 2.0
+	 * end of section 5.6.3) have wMaxPacketSize = 0.
+	 * So don't warn about those.
 	 */
 	maxp = le16_to_cpu(endpoint->desc.wMaxPacketSize);
-	if (maxp == 0 && !(usb_endpoint_xfer_isoc(d) && asnum == 0)) {
+
+	if (maxp == 0 && bcdUSB != 0x0220 &&
+	    !(usb_endpoint_xfer_isoc(d) && asnum == 0))
 		dev_notice(ddev, "config %d interface %d altsetting %d endpoint 0x%X has invalid wMaxPacketSize 0\n",
 		    cfgno, inum, asnum, d->bEndpointAddress);
-	}
 
 	/* Find the highest legal maxpacket size for this endpoint */
 	i = 0;		/* additional transactions per microframe */
@@ -465,6 +500,12 @@ static int usb_parse_endpoint(struct device *ddev, int cfgno,
 				maxp);
 	}
 
+	/* Parse a possible eUSB2 periodic endpoint companion descriptor */
+	if (bcdUSB == 0x0220 && d->wMaxPacketSize == 0 &&
+	    (usb_endpoint_xfer_isoc(d) || usb_endpoint_xfer_int(d)))
+		usb_parse_eusb2_isoc_endpoint_companion(ddev, cfgno, inum, asnum,
+							endpoint, buffer, size);
+
 	/* Parse a possible SuperSpeed endpoint companion descriptor */
 	if (udev->speed >= USB_SPEED_SUPER)
 		usb_parse_ss_endpoint_companion(ddev, cfgno,