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([2001:a61:131b:7001:9072:e882:13e9:40fa]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-426ce583316sm17384481f8f.20.2025.10.13.02.29.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Oct 2025 02:29:00 -0700 (PDT) Message-ID: <194258bf-e78c-46b8-8229-3b019f2b8ab0@suse.com> Date: Mon, 13 Oct 2025 11:28:59 +0200 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: ttyACM versus ttyUSB To: Alex Henrie , Greg KH Cc: linux-usb@vger.kernel.org, Johan Hovold , vojtech@suse.cz References: <2025101243-ongoing-truce-3aa5@gregkh> <2025101238-mastiff-decibel-4b4f@gregkh> Content-Language: en-US From: Oliver Neukum In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 12.10.25 21:01, Alex Henrie wrote: > I did notice that the ACM protocol has no way to set the baud rate or > read the CTS line and I wondered if those limitations were the reason > for keeping its driver separate. Today there are ttyUSB drivers that > likewise have limitations on the baud rate and the flow control lines > (some are even based on ACM), but they weren't around in 1999, so I > can see how the difference in capabilities would have been another > motivation for the difference in naming conventions. You could argue that ACM is intended to be a driver for a _modem_ , not a serial line. In principle we are trying to propagate a layering violation that is so old that we no longer see it as a violation. Regards Oliver