When fetching the first descriptor from a new device, only validate that
we received at least 8 bytes, not that we received the entire descriptor.
The reasoning is:
- The code only uses fields in the first 8 bytes, so that's all we need
to have fetched at this stage.
- The smallest maxpacket size is 8 bytes. Before we know the actual
maxpacket the device uses, the USB controller may only accept a single
packet (see the DWC2 note in the comment added in the commit).
Consequently we are only guaranteed to receive 1 packet (at least 8
bytes) even in a non-error case.
Fixes: 1a7758044b04 ("usb: Early failure when the first descriptor read
fails or is invalid")
Cc: Paul Kocialkowski <cont...@paulk.fr>
Signed-off-by: Stephen Warren <swar...@wwwdotorg.org>
---
common/usb.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/common/usb.c b/common/usb.c
index f6488475a7f2..bf76c4159341 100644
--- a/common/usb.c
+++ b/common/usb.c
@@ -956,7 +956,22 @@ int usb_new_device(struct usb_device *dev)
*/
#ifndef CONFIG_USB_XHCI
err = usb_get_descriptor(dev, USB_DT_DEVICE, 0, desc, 64);
- if (err < sizeof(struct usb_device_descriptor)) {
+ /*
+ * Validate we've received only at least 8 bytes, not that we've
+ * received the entire descriptor. The reasoning is:
+ * - The code only uses fields in the first 8 bytes, so that's all we
+ * need to have fetched at this stage.
+ * - The smallest maxpacket size is 8 bytes. Before we know the actual
+ * maxpacket the device uses, the USB controller may only accept a
+ * single packet. Consequently we are only guaranteed to receive 1
+ * packet (at least 8 bytes) even in a non-error case.
+ *
+ * At least the DWC2 controller needs to be programmed with the number
+ * of packets in addition to the number of bytes. A request for 64
+ * bytes of data with the maxpacket guessed as 64 (above) yields a
+ * request for 1 packet.
+ */
+ if (err < 8) {
debug("usb_new_device: usb_get_descriptor() failed\n");
return -EIO;
}
--
1.9.1
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