From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f46.google.com (mail-wr1-f46.google.com [209.85.221.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 453DB2EBBBE for ; Wed, 16 Jul 2025 08:29:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.46 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752654572; cv=none; b=KXip9M+CluqCamwKXvLv/dSbFvYSGwUncQG+VRQ7fbnaeRhKY+pttOeblyNyYwpC+3ykWc3aq14HS1C13+PFKo3nMgWDS+Cp5S5KSFqVrSk5EadrJxi0OzYZgb362hL8KS1F1ScjKBucSIJ+xPSf6Thlb5XwVAeUkc5pZfCoL8k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752654572; c=relaxed/simple; bh=/dVOnKYB8CD/wyyHbMWcCAYLrsRBtnjmn40w6cFnUfA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZaPWa6x9LhpD+W9jSUKyYugxIpxs9y7qcIkNCNvtXxi5MFOuMtABToDQZF95btdyJpwmQ4DR2097OeiI4jb0JkRtJxHbG9w/dgqHY5wU4NspFUYtIEqmuDV4inbNNyts7Mw11ivArYKM9bz8pyGcz/aZC5zrpbiqLIbLAytqris= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=TJ+DqaZf; arc=none smtp.client-ip=209.85.221.46 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="TJ+DqaZf" Received: by mail-wr1-f46.google.com with SMTP id ffacd0b85a97d-3a575a988f9so3671397f8f.0 for ; Wed, 16 Jul 2025 01:29:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1752654568; x=1753259368; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=kTS987hZr2/BPWLmY8oveEZ2X67lASpu1Bb54ts50jo=; b=TJ+DqaZfl0zIkqswkSGb6b5pGV9HjXtR9W602M0rVQSG5DF65rjluDPe+4ILj9b0xD dQdGk+32aL1h6rxwo/lmrOc4pUZ/8LUMZ9u/noYWD8KZMRM/qJS6PorYHnu35IVMgeyS 9tmAiw9zyY+Y4or08t2QxQm3vpQiZKYyy4yfMlJ8QqYvxbXa1q5KVodNevEzG0lpvLWf zVyAR/H006nurUAGEEZx0AmFMCLmEPeXsYjPfhOW9OASpo3W5S1WX5WSgE1/ZhwYWtlo EDtoSWGFOyIDh2xOD0LCgtbPQhm3fDnEMIg9faXtbQICCpUH3uJflijVdayK9HDzQGbj ZyNQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1752654568; x=1753259368; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=kTS987hZr2/BPWLmY8oveEZ2X67lASpu1Bb54ts50jo=; b=rJIQLzslG30iV+cz7xQxK+N2UBr1bL00WsRlhTXKQCZ/Z1ROvgETLcLaN/vX+TEzhm 5t2KN276oUlYVzvsT/02Cki96fDoS95MojnsRgzHts8qRvR2rXk137DmLKdaKjuW7jsP hJaSw8ntu1MyU3Xcc6BW9Syp+/Lg0rp5qZ1xcYqMTuF4rZiDvQ4K/0fKhSfBd3E688NK W4Tjv5CqDLvRyd/s7mvR/9qYmelJLcI9oOTV98+p3qPb0I/H6K8v9v12W0i7v66X+LNQ kXA+Y2ASmo8/9+0KNz+HzIkTPoAsnCLdjx7PMoykm/dhjXlDkL7Xd43xLCGDviTHBB2o tC8A== X-Forwarded-Encrypted: i=1; AJvYcCX8slzTtM+urC9tri95TyQX4yIQJ2gRCGfYitaBK7aUZIRzmdNbRk1tDyAv+QunKWONyhpzg0n0dgqHgG4=@vger.kernel.org X-Gm-Message-State: AOJu0YyGSl0AB8MaIFOjU8V0fAe++jFyucRm92Wah2qsIigNtqOBXvqD w1CtIKlWX2l/QvqTIhik8RJkus7y+fu6SEsIkwqXEvXYe0w7sSVzoJG9SzkPFk0x23c= X-Gm-Gg: ASbGncscZY5Q82B/QuEK3+2bRNdzhcRk8dGgdEfESi8GaXDUYfKZqCKJChAaW9BIERT e68fxzKRb2s/GFRzY75mGFtulyqBLGNHVQgK7vxZ8nK4/zSsjNRTR2vVNIIkBMFN171QXQvrdUu RaQuQ6bId5xiGiRMtlFA96kEYIaPrvCJG1ijswvkmrKgbHOtueCZIDTwwt3QTn1tyan26Qu/nd5 u0qnuywuA4aRFvNI4IdeuD6YVOUsjDQk6HF5WScxmGxkYUAWXV0dR0kFTZOMNASC6iPSxFXD7ne q8NDa07g9tD9HkFgwyzi65efpzYTiJ1M/ivJpjhXVW7k9acTjlTvNfzTmKdaXgFRD1Yy91rc6GY DV4IXHtdw8X94XGa0XHyGca4bJQ99IE2wHNXFmn0V6051rJbHLdhEILvKuMqr9LhF6g== X-Google-Smtp-Source: AGHT+IFSZH4omeTXZAl7Lh2gjNFC0tMnhjbsZXaH62GbzEcddv2hbbklP4Avf1fLgsmVBRMpxR52/g== X-Received: by 2002:adf:9ccb:0:b0:3a5:39d7:3f17 with SMTP id ffacd0b85a97d-3b60dd898c7mr1162606f8f.47.1752654568473; Wed, 16 Jul 2025 01:29:28 -0700 (PDT) Received: from ?IPV6:2001:a61:133f:9e01:b1a5:79c8:d196:e761? ([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-kernel@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