From: Sergei Shtylyov <sergei.shtylyov@gmail.com>
To: Matthias-Christian Ott <ott@mirix.org>,
Petko Manolov <petkan@nucleusys.com>
Cc: linux-usb@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH] net: usb: pegasus: Do not drop long Ethernet frames
Date: Mon, 27 Dec 2021 12:56:41 +0300 [thread overview]
Message-ID: <36ee5c5c-a03c-c9f5-dd5c-9e3a04b0374a@gmail.com> (raw)
In-Reply-To: <20211226132930.7220-1-ott@mirix.org>
Hello!
On 26.12.2021 16:29, 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
^^^^^ ^^^^^
Too many limits. :-)
> 1536 octets (PEGASUS_MTU).
>
> Signed-off-by: Matthias-Christian Ott <ott@mirix.org>
[...]
MBR, Sergey
next prev parent reply other threads:[~2021-12-27 9:56 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-26 13:29 [PATCH] net: usb: pegasus: Do not drop long Ethernet frames Matthias-Christian Ott
2021-12-26 15:39 ` Andrew Lunn
2021-12-26 16:01 ` Matthias-Christian Ott
2021-12-26 16:31 ` Andrew Lunn
2021-12-26 22:21 ` Matthias-Christian Ott
2021-12-26 22:28 ` Petko Manolov
2021-12-27 9:56 ` Sergei Shtylyov [this message]
2022-01-02 14:22 ` Matthias-Christian Ott
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