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 774ED3451CA; Wed, 12 Nov 2025 17:12:14 +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=1762967535; cv=none; b=NQ7oUA3eh78tDJHy9E9Fe/YCQPr2UTLnwpoIub1RpGSLwsVa0l+zL7vBsEKnLcCwJHdrvqBa+iINY97/qQvacGkOhTAO3YBX+4WVehEmhwYudG+cYnZ2MsC228HB/Ie9nz857Uu2h71mNDqD0Hs+8/8tgffp9DuTBtlFcEhYcQo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762967535; c=relaxed/simple; bh=LfwDw5nDHN9mjQ61ppHmMZFw8Tz8l0KhDqOCjnLSsZs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=g9vHbF18bmmneTHi6wc8HNZXGMzJ97E1fgekDIrmapSSQB7q4zy1ggivBNqlsmehdPWPp5OMMN7EPw3Aw3on/P4UdNJTsfc7HJ+/tWHlErZBLdaVzRa7wsub8lMkYhljgwq8wRvsAcuFnbLp3z0OyiqYsMlzR/AyFsabino30fo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=KTYxyHGT; 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="KTYxyHGT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C0021C113D0; Wed, 12 Nov 2025 17:12:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1762967533; bh=LfwDw5nDHN9mjQ61ppHmMZFw8Tz8l0KhDqOCjnLSsZs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KTYxyHGTfO4RZ7Qp+aEhY9+SN67VWZDd2oFFjjTfeAaciwJQIETuyG3VBpSKtwpeE MPDhM71JtUblUCmp8YZVjUEVNwdCsrJ9CCW9xAme1tvzqI1vdSMVDqCcoZlu7cR83o 7OYGS2MbE1Df5kVTccsRCPaZegHiw6nKxsc83dd0= Date: Wed, 12 Nov 2025 11:46:50 -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: <2025111241-domestic-moonstone-f75f@gregkh> References: <20251110033556.GC2988753@mit.edu> <20251110201933.GH2988753@mit.edu> <0F8021E8-F288-4669-8195-9948844E36FD@zytor.com> <20251111035143.GJ2988753@mit.edu> <2025111214-doily-anyway-b24b@gregkh> <6DBB5931-ACD4-4174-9FCE-96C45FFC4603@zytor.com> 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: <6DBB5931-ACD4-4174-9FCE-96C45FFC4603@zytor.com> On Wed, Nov 12, 2025 at 08:09:45AM -0800, H. Peter Anvin wrote: > On November 12, 2025 3:22:56 AM PST, Greg KH wrote: > >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 > > Ugh. > > I have made it very clear that I am very aware that there is broken hardware. I would posit that there is NO "non-broken" usb->serial devices out there. The closest I have seen was the old IO-Edgeport devices, but they were expensive and got bought out by some other company and in the end didn't succeed due to all of the "cheap" devices/chips out there that just did dumb tx/rx transfers over a fake serial connection. > What I'm trying to do is to deal with the (occasional) case of > *non*-broken hardware. Right now Linux breaks the non-broken hardware > for it, and I don't think the existence of broken hardware is a good > justification for that. No, but we have to handle both somehow. And given that we still get brand-new UART drivers sent to use every few months, there is just more and more "broken" hardware out there overall. Anyway, good luck coming up with a scheme to handle your crazy connections, I would push back and say "any device that treats a serial control line as a power signal is broken to start with" :) greg k-h