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usb: Only get 64 bytes device descriptor for full speed devices

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Full speed device endpoint 0 can have 8/16/32/64 bMaxPacketSize0.
Other speed devices report fixed value per USB spec. So it only
makes sense if we send a get device descriptor with 64 bytes to
full speed devices.

While we are here, update the comment block to be within 80 cols.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
This commit is contained in:
Bin Meng 2017-09-18 06:40:42 -07:00 committed by Marek Vasut
parent 1897d60130
commit c008faa773
1 changed files with 15 additions and 14 deletions
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29
common/usb.c
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@ -970,23 +970,24 @@ static int usb_setup_descriptor(struct usb_device *dev, bool do_read)
dev->epmaxpacketin[0] = dev->descriptor.bMaxPacketSize0;
dev->epmaxpacketout[0] = dev->descriptor.bMaxPacketSize0;
if (do_read) {
if (do_read && dev->speed == USB_SPEED_FULL) {
int err;
/*
* 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.
* 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.
* 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.
*/
err = get_descriptor_len(dev, 64, 8);
if (err)
@ -1009,7 +1010,7 @@ static int usb_setup_descriptor(struct usb_device *dev, bool do_read)
dev->maxpacketsize = PACKET_SIZE_64;
break;
default:
printf("usb_new_device: invalid max packet size\n");
printf("%s: invalid max packet size\n", __func__);
return -EIO;
}