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From: Greg KH <gregkh@linuxfoundation.org>
To: Alex Henrie <alexhenrie24@gmail.com>
Cc: linux-usb@vger.kernel.org, oneukum@suse.com,
	Johan Hovold <johan@kernel.org>,
	vojtech@suse.cz
Subject: Re: ttyACM versus ttyUSB
Date: Sun, 12 Oct 2025 08:07:35 +0200	[thread overview]
Message-ID: <2025101243-ongoing-truce-3aa5@gregkh> (raw)
In-Reply-To: <CAMMLpeRU72CMxHdF-rO9y1Nvzj9nPnuQTOZWcCrM4fOJ1byacw@mail.gmail.com>

On Sat, Oct 11, 2025 at 11:00:00PM -0600, Alex Henrie wrote:
> Dear kernel developers,
> 
> I am very curious and I haven't been able to find a definitive answer
> anywhere: Why is the cdc-acm driver separate from the general
> usbserial driver? There are lots of drivers that use usbserial, each
> with its own unique protocol. What makes ACM so special that it needs
> to be separated out as /dev/ttyACM* instead of going with everything
> else in /dev/ttyUSB*?
> 
> I can think of several possible reasons, but I'd really like to know
> what reasons matter to the kernel architects/maintainers.

cdc-acm implements the USB specification for that protocol, which is
defined by the USB group.  All of the usb-serial drivers do NOT follow
that protocol and use their own vendor-specific ways of talking to the
device.

Hope this helps,

greg k-h

  reply	other threads:[~2025-10-12  6:07 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-10-12  5:00 ttyACM versus ttyUSB Alex Henrie
2025-10-12  6:07 ` Greg KH [this message]
2025-10-12 15:55   ` Alex Henrie
2025-10-12 16:21     ` Greg KH
2025-10-12 19:01       ` Alex Henrie
2025-10-12 19:53         ` Greg KH
2025-10-12 22:40           ` Alex Henrie
2025-10-13  9:28         ` Oliver Neukum
2025-10-13 10:47           ` Vojtech Pavlik
2025-10-13 15:42             ` Alex Henrie
2025-10-13 16:14               ` Greg KH

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