From: Alan Stern stern@rowland.harvard.edu
commit 2548288b4fb059b2da9ceada172ef763077e8a59 upstream.
It turns out that even though endpoints with a maxpacket length of 0 aren't useful for data transfer, the descriptors do serve other purposes. In particular, skipping them will also skip over other class-specific descriptors for classes such as UVC. This unexpected side effect has caused some UVC cameras to stop working.
In addition, the USB spec requires that when isochronous endpoint descriptors are present in an interface's altsetting 0 (which is true on some devices), the maxpacket size _must_ be set to 0. Warning about such things seems like a bad idea.
This patch updates an earlier commit which would log a warning and skip these endpoint descriptors. Now we only log a warning, and we don't even do that for isochronous endpoints in altsetting 0.
We don't need to worry about preventing endpoints with maxpacket = 0 from ever being used for data transfers; usb_submit_urb() already checks for this.
Reported-and-tested-by: Roger Whittaker Roger.Whittaker@suse.com Fixes: d482c7bb0541 ("USB: Skip endpoints with 0 maxpacket length") Signed-off-by: Alan Stern stern@rowland.harvard.edu CC: Laurent Pinchart laurent.pinchart@ideasonboard.com Link: https://marc.info/?l=linux-usb&m=157790377329882&w=2 Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.2001061040270.1514-100000@iolanthe... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/usb/core/config.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
--- a/drivers/usb/core/config.c +++ b/drivers/usb/core/config.c @@ -358,12 +358,16 @@ static int usb_parse_endpoint(struct dev endpoint->desc.wMaxPacketSize = cpu_to_le16(8); }
- /* Validate the wMaxPacketSize field */ + /* + * 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. + */ maxp = usb_endpoint_maxp(&endpoint->desc); - if (maxp == 0) { - dev_warn(ddev, "config %d interface %d altsetting %d endpoint 0x%X has wMaxPacketSize 0, skipping\n", + if (maxp == 0 && !(usb_endpoint_xfer_isoc(d) && asnum == 0)) { + dev_warn(ddev, "config %d interface %d altsetting %d endpoint 0x%X has invalid wMaxPacketSize 0\n", cfgno, inum, asnum, d->bEndpointAddress); - goto skip_to_next_endpoint_or_interface_descriptor; }
/* Find the highest legal maxpacket size for this endpoint */