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([2001:a61:133f:9e01:b1a5:79c8:d196:e761]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3b5e8e1e332sm17275063f8f.79.2025.07.16.01.29.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Jul 2025 01:29:28 -0700 (PDT) Message-ID: Date: Wed, 16 Jul 2025 10:29:27 +0200 Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: USB cdc-acm driver: break and command To: "H. Peter Anvin" , Oliver Neukum Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, Jiri Slaby , linux-serial@vger.kernel.org References: Content-Language: en-US From: Oliver Neukum In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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