Re: [PATCH net v2] net: usb: pegasus: Do not drop long Ethernet frames
flat view
From: Petko Manolov <petkan@nucleusys.com>
Date: 2021-12-27 11:11:49
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linux-usb
On 21-12-26 23:12:08, Matthias-Christian Ott wrote:
The D-Link DSB-650TX (2001:4002) is unable to receive Ethernet frames that are longer than 1518 octets, for example, Ethernet frames that contain 802.1Q VLAN tags. The frames are sent to the pegasus driver via USB but the driver discards them because they have the Long_pkt field set to 1 in the received status report. The function read_bulk_callback of the pegasus driver treats such received "packets" (in the terminology of the hardware) as errors but the field simply does just indicate that the Ethernet frame (MAC destination to FCS) is longer than 1518 octets. It seems that in the 1990s there was a distinction between "giant" (> 1518) and "runt" (< 64) frames and the hardware includes flags to indicate this distinction. It seems that the purpose of the distinction "giant" frames was to not allow infinitely long frames due to transmission errors and to allow hardware to have an upper limit of the frame size. However, the hardware already has such limit with its 2048 octet receive buffer and, therefore, Long_pkt is merely a convention and should not be treated as a receive error. Actually, the hardware is even able to receive Ethernet frames with 2048 octets which exceeds the claimed limit frame size limit of the driver of 1536 octets (PEGASUS_MTU).
2048 is not mentioned anywhere in both, adm8511 and adm8515 documents. In the latter I found 1638 as max packet length, but that's not the default. The default is 1528 and i don't feel like changing it without further investigation. Thus, i assume it is safe to change PEGASUS_MTU to 1528 for the moment. VLAN frames have 4 additional bytes so we aren't breaking neither pegasus I nor pegasus II devices. If you're going to make ver 3 of this change, you might as well modify PEGASUS_MTU in pegasus.h as a separate patch within the same series. Petko
quoted hunk ↗ jump to hunk
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Matthias-Christian Ott <redacted> --- V1 -> V2: Included "Fixes:" tag drivers/net/usb/pegasus.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)diff --git a/drivers/net/usb/pegasus.c b/drivers/net/usb/pegasus.c index 140d11ae6688..2582daf23015 100644 --- a/drivers/net/usb/pegasus.c +++ b/drivers/net/usb/pegasus.c@@ -499,11 +499,11 @@ static void read_bulk_callback(struct urb *urb) goto goon; rx_status = buf[count - 2]; - if (rx_status & 0x1e) { + if (rx_status & 0x1c) { netif_dbg(pegasus, rx_err, net, "RX packet error %x\n", rx_status); net->stats.rx_errors++; - if (rx_status & 0x06) /* long or runt */ + if (rx_status & 0x04) /* runt */ net->stats.rx_length_errors++; if (rx_status & 0x08) net->stats.rx_crc_errors++;-- 2.30.2