Hi Alan,
Thank you for the patch.
On Mon, Jan 06, 2020 at 10:43:42AM -0500, Alan Stern wrote:
> 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@xxxxxxxx>
> Fixes: d482c7bb0541 ("USB: Skip endpoints with 0 maxpacket length")
> Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
> CC: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Link: https://marc.info/?l=linux-usb&m=157790377329882&w=2
The patch looks good to me, so
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
But shouldn't we also warn if maxp != 0 && usb_endpoint_xfer_isoc(d) &&
asnum == 0 ?
> ---
>
>
> [as1928]
>
>
> drivers/usb/core/config.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> Index: usb-devel/drivers/usb/core/config.c
> ===================================================================
> --- usb-devel.orig/drivers/usb/core/config.c
> +++ usb-devel/drivers/usb/core/config.c
> @@ -346,12 +346,16 @@ 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 */
--
Regards,
Laurent Pinchart
