linux-kernel - Re: USB cdc-acm driver: break and command

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Message-ID: <2025071652-afar-cornhusk-0830@gregkh>
Date: Wed, 16 Jul 2025 08:58:10 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: Oliver Neukum <oneukum@...e.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
	linux-serial@...r.kernel.org
Subject: Re: USB cdc-acm driver: break and command

On Tue, Jul 15, 2025 at 02:00:10PM -0700, H. Peter Anvin wrote:
> Hi,
> 
> I noticed looking at the CDC-ACM driver that it uses the assert/local
> delay/deassert method of sending BREAK.  Given that the CDC model has a
> delay specifier in the command packet, is there any reason not to set
> TTY_DRIVER_HARDWARE_BREAK and sending only one packet?
> 
> I'm also wondering if it would make sense to support the
> SEND_ENCAPSULATED_COMMAND and GET_ENCAPSULATED_RESPONSE commands, presumably
> via an ioctl().  I'm not 100% sure because I'm not sure there aren't
> potential security issues.
> 
> I'm guessing both of these could be of some use to embedded devices that
> emulate a ttyACM serial port.

No idea why this is that way, sorry.  Try making the change and see if
it actually works?

thanks,

greg k-h