linux-kernel - Re: RFC: Serial port DTR/RTS

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Message-ID: <6DBB5931-ACD4-4174-9FCE-96C45FFC4603@zytor.com>
Date: Wed, 12 Nov 2025 08:09:45 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: "Theodore Ts'o" <tytso@....edu>, Maarten Brock <Maarten.Brock@...ls.nl>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: RFC: Serial port DTR/RTS - O_NRESETDEV

On November 12, 2025 3:22:56 AM PST, Greg KH <gregkh@...uxfoundation.org> 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. 

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.