Re: USB cdc-acm driver: break and command

[Oliver Neukum]

On 15.07.25 23:00, 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?

1. The existing code is tested and usually works.
2. The locking goes away. I have no idea what happens if you are
sending a second break while a break is still going on.

> 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.

Well, one of the purposes of the CDC-ACM driver is to hide that
you are talking to a USB device.
In theory we could do that. I don't quite see the value.
Sending arbitrary data from user space to a control endpoint
does not make me happy.

	HTH
		Oliver