linux-kernel - Re: [PATCH v3] net/can/gs_usb: increase max interface to U8

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Message-ID: <7d35d8ca-f711-41b2-b058-08a19a207160@kernel.org>
Date: Tue, 30 Sep 2025 14:44:55 +0900
From: Vincent Mailhol <mailhol@...nel.org>
To: Celeste Liu <uwu@...lacanthus.name>
Cc: Maximilian Schneider <max@...neidersoft.net>,
 Henrik Brix Andersen <henrik@...xandersen.dk>,
 Wolfgang Grandegger <wg@...ndegger.com>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-can@...r.kernel.org,
 linux-kernel@...r.kernel.org, Runcheng Lu <runcheng.lu@...icro.com>,
 stable@...r.kernel.org, Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: [PATCH v3] net/can/gs_usb: increase max interface to U8_MAX

On 9/30/25 12:06 PM, Celeste Liu wrote:
> This issue was found by Runcheng Lu when develop HSCanT USB to CAN FD
> converter[1]. The original developers may have only 3 intefaces device to
                                                        ^^^^^^^^^
interfaces (missing "r")

> test so they write 3 here and wait for future change.
> 
> During the HSCanT development, we actually used 4 interfaces, so the
> limitation of 3 is not enough now. But just increase one is not
> future-proofed. Since the channel type in gs_host_frame is u8, just
> increase interface number limit to max size of u8 safely.
> 
> [1]: https://github.com/cherry-embedded/HSCanT-hardware
> 
> Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
> Reported-by: Runcheng Lu <runcheng.lu@...icro.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Celeste Liu <uwu@...lacanthus.name>

Reviewed-by: Vincent Mailhol <mailhol@...nel.org>

The patch is good as-is. However, speaking of the interface numbers, there is
another issue in this gs_usb driver: net_device->dev_port is not populated, and
according to the documentation, this is a bug.

See the description here:

  https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-net

  What:		/sys/class/net/<iface>/dev_port

  Date:		February 2014

  KernelVersion:	3.15

  Contact:	netdev@...r.kernel.org

  Description:

  		Indicates the port number of this network device, formatted

  		as a decimal value. Some NICs have multiple independent ports

  		on the same PCI bus, device and function. This attribute allows

  		userspace to distinguish the respective interfaces.

  		Note: some device drivers started to use 'dev_id' for this

  		purpose since long before 3.15 and have not adopted the new

  		attribute ever since. To query the port number, some tools look

  		exclusively at 'dev_port', while others only consult 'dev_id'.

  		If a network device has multiple client adapter ports as

  		described in the previous paragraph and does not set this

  		attribute to its port number, it's a kernel bug.

Would you mind sending a separate patch (with a Fixes: tag) to resolve this?

Yours sincerely,
Vincent Mailhol