Bjørn Mork <bjorn@xxxxxxx> writes:
> I have another issue with the Sierra firmware which I hope you can help
> me with: The MC7710 device requires at ZLP even if we send
> dwNtbOutMaxSize sized NTBs. This is a problem because the current code
> explicitly prevents this.
If anyone found this more than normally confused, then that is
correct...
What the NCM code does is that it sends a *short* packet whenever the
usbnet would normally have done so, except if the NTP length >=
dwNtbOutMaxSize.
The problem is that we do not set
urb->transfer_flags |= URB_ZERO_PACKET;
either in this special case, resulting in neither a short nor a zero
length packet being sent. I believe this is what the Sierra firmware
chokes at. This seems to fix the issue, and is IMHO correct:
diff --git a/drivers/net/usb/cdc_mbim.c b/drivers/net/usb/cdc_mbim.c
index 42f51c7..3a5673a 100644
--- a/drivers/net/usb/cdc_mbim.c
+++ b/drivers/net/usb/cdc_mbim.c
@@ -366,7 +366,7 @@ err:
static const struct driver_info cdc_mbim_info = {
.description = "CDC MBIM",
- .flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN,
+ .flags = FLAG_NO_SETINT | FLAG_MULTI_PACKET | FLAG_WWAN | FLAG_SEND_ZLP,
.bind = cdc_mbim_bind,
.unbind = cdc_mbim_unbind,
.manage_power = cdc_mbim_manage_power,
But I wonder if this isn't really a generic problem in usbnet. The
FLAG_MULTI_PACKET test here seems completely bogus:
if (length % dev->maxpacket == 0) {
if (!(info->flags & FLAG_SEND_ZLP)) {
if (!(info->flags & FLAG_MULTI_PACKET)) {
urb->transfer_buffer_length++;
if (skb_tailroom(skb)) {
skb->data[skb->len] = 0;
__skb_put(skb, 1);
}
}
} else
urb->transfer_flags |= URB_ZERO_PACKET;
}
Either the FLAG_MULTI_PACKET minidriver will have already padded the
buffer so that we do not hit (length % dev->maxpacket == 0), or we
should choose one of the alternatives: ZLP or padding.
Minidrivers not wanting the short packets (like cdc_ncm) must set
FLAG_SEND_ZLP.
Bjørn
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