On 1/30/26 11:54 AM, Jonas Karlman wrote:
Hello Jonas,
Change to use a fixed URB buffer size of 16 KiB to fix use of Ethernet,
Why 16 kiB and not something else ?
Using anything larger than 16 KiB resulted in issues, and a datasheet
for the older AX88772 prior to the D revision mention default 16 KiB for
"Maximum Frame Burst transfer on USB bus" so 16 KiB seemed like a safe
size to use for newer revisions, and this also made it possible to use
fragmented packets up to just below 16 KiB.
Please include this information in the commit message.
Is this a USB controller related problem/limitation ? Maybe the DWC2
driver needs fixing instead, to handler larger buffers ?
I accidentally mixed up what host controller was being used, the board in
question is using a generic-echi controller not the DWC2 as I stated.
Below follow some debug prints, what can be observed is that when
length=26624 is returned from ehci_submit_bulk_msg the ax88179_eth_recv
will return len >16 KiB and that result in the rx_hdr at the end of
the returned buffer being bogus data, e.g. for following:
BOOTP broadcast 1
** asix_send_common(), len 342
ehci_submit_bulk_msg: dev='usb@ff100000', udev=00000000f9f2c520
dev=00000000f9f2c520, pipe=c0018303, buffer=00000000f9ee0680, length=350,
req=0000000000000000
TOKEN=0x80008c00
Tx: len = 346, actual = 350, err = 0
ax88179_eth_recv: first try, len=0
ehci_submit_bulk_msg: dev='usb@ff100000', udev=00000000f9f2c520
dev=00000000f9f2c520, pipe=c0010383, buffer=00000000f9f2cf00, length=26624,
req=0000000000000000
TOKEN=0xa7808d00
ax88179_eth_recv: second try, len=16512
ax88179_eth_recv: 2 packets received, pkt header at 112
ax88179_eth_recv: return packet of 106 bytes (1 packets left)
ax88179_eth_recv: return packet of 0 bytes (0 packets left)
The buffers returned from the AX88179 contains something like:
<packet data N><N+1>... <packet header N><N+1>... <RX HDR>
Above the "2 packets received, pkt header at 112" seem to indicate that
the pkt header is in the middle of the packet data, in other instances
the rx_hdr seem to indicate that the buffer contains thousands of
packets, i.e. the rx_hdr is likely bogus when more than 16 KiB is
returned from ehci_submit_bulk_msg.
Is this maybe some wrap-around ? 16 kiB x4 is 65536 , which is 16bit limit.
