From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0780E2C15BE; Wed, 12 Nov 2025 11:22:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762946578; cv=none; b=adoxFo5GloITWfVTQ4Jd+Te0IPCr3yS0RpSRHkS5p5504cERscBdNAltLuD6e7cbjcffhLv+TQD3nRJVq6+d9dHDPIPjmyEEcvYmFA7ncN6Li/RwA1JpHMFI8CGoeLoPg8YSMh9aeufES9LAPprXT4ZzwZgXHVp5lBgUPsbt650= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762946578; c=relaxed/simple; bh=hjXB8IW77oxvUB9X1HvFeAFgisSOfgJqp9S36dCalM8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=RZhZaWUJBO9eMVmG4eC98DchtFt1zdRZfVWwL4UCmVgK/HR/57v3yDE1JnmPWvL9nekmzzlpxN7E0ags48GEKHIe+WLecvf2zsHPXIaec3FYSjyEMtMAVWtdogWWkJ2nJ0q7MADX2trSBKGTsH6QyX/GXNf9KvduKpX6IrRuFwM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=MIhBGJIM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="MIhBGJIM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6AF2FC4CEF5; Wed, 12 Nov 2025 11:22:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1762946577; bh=hjXB8IW77oxvUB9X1HvFeAFgisSOfgJqp9S36dCalM8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MIhBGJIM2U45fn4oiaiLg6XOt+xA9as4EGD3E4pm2UXNIw/neuqegu9zwE7KGDtg3 d/DOg4MDqHIJuerXZnzxxUVFZh6E3FgwAKRFHnS3rCdq9fGKWlXHe+ygUWAGJsehlR DHc3EgzAtD2+FW6tEdtJDzqrq6bdhp6p6LVAlYyw= Date: Wed, 12 Nov 2025 06:22:56 -0500 From: Greg KH To: "H. Peter Anvin" Cc: Theodore Ts'o , Maarten Brock , "linux-serial@vger.kernel.org" , "linux-api@vger.kernel.org" , LKML Subject: Re: RFC: Serial port DTR/RTS - O_NRESETDEV Message-ID: <2025111214-doily-anyway-b24b@gregkh> References: <20251107173743.GA3131573@mit.edu> <20251110033556.GC2988753@mit.edu> <20251110201933.GH2988753@mit.edu> <0F8021E8-F288-4669-8195-9948844E36FD@zytor.com> <20251111035143.GJ2988753@mit.edu> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Nov 10, 2025 at 07:57:22PM -0800, H. Peter Anvin wrote: > Honestly, though, I'm far less interested in what 8250-based hardware does than e.g. USB. hahahahahahaha {snort} Hah. that's a good one. Oh, you aren't kidding. Wow, good luck with this. USB-serial adaptors are all over the place, some have real uarts in them (and so do buffering in the device, and line handling in odd ways when powered up), and some are almost just a straight pipe through to the USB host with control line handling ideas tacked on to the side as an afterthought, if at all. There is no standard here, they all work differently, and even work differently across the same device type with just barely enough hints for us to determine what is going on. So don't worry about USB, if you throw that into the mix, all bets are off and you should NEVER rely on that. Remeber USB->serial was explicitly rejected by the USB standard group, only to have it come back in the "side door" through the spec process when it turned out that Microsoft hated having to write a zillion different vendor-specific drivers because the vendor provided ones kept crashing user's machines. So what we ended up with was "just enough" to make it through the spec process, and even then line signals are probably never tested so you can't rely on them. good luck! greg "this brought up too many bad memories" k-h