linux-kernel - Re: [PATCH tty-next v3 1/6] serial: 8250: Adjust the timeout for FIFO mode

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.21.2411010102150.40463@angie.orcam.me.uk>
Date: Fri, 1 Nov 2024 01:24:53 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: John Ogness <john.ogness@...utronix.de>
cc: Jiri Slaby <jirislaby@...nel.org>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Petr Mladek <pmladek@...e.com>, 
    Sergey Senozhatsky <senozhatsky@...omium.org>, 
    Steven Rostedt <rostedt@...dmis.org>, Thomas Gleixner <tglx@...utronix.de>, 
    Esben Haabendal <esben@...nix.com>, linux-serial@...r.kernel.org, 
    linux-kernel@...r.kernel.org, 
    Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
    Rengarajan S <rengarajan.s@...rochip.com>, 
    Jeff Johnson <quic_jjohnson@...cinc.com>, 
    Serge Semin <fancer.lancer@...il.com>, 
    Lino Sanfilippo <l.sanfilippo@...bus.com>, 
    Wander Lairson Costa <wander@...hat.com>
Subject: Re: [PATCH tty-next v3 1/6] serial: 8250: Adjust the timeout for
 FIFO mode

On Thu, 31 Oct 2024, John Ogness wrote:

> >> THRE only signals there is a space for one character.
> >
> >  Nope[1]:
> >
> > "In the FIFO mode, THRE is set when the transmit FIFO is empty; it is 
> > cleared when at least one byte is written to the transmit FIFO."
> >
> > It seems common enough a misconception that once I actually had to fix the 
> > bad interpretation of THRE in an unpublished platform driver to get decent 
> > performance out of it at higher rates such as 230400bps, as it only pushed 
> > one byte at a time to the FIFO while it had it all available once THRE has 
> > been set.
> 
> I do not know if this is true for all 8250-variants. If there is some
> variant where it functions as Jiri expected, then it would mean
> significant text loss during longer messages. But that would already be
> a problem in the current mainline driver.

 Or rather in my case it would prevent communication from working at all; 
I actually had to fix the issue for networking over a serial line rather 
than just exchanging text messages, and hence a particular need to make it 
run fast.

 I don't expect any 550 clone to work in a different manner, but I find 
the TI manual particularly unambiguous and well-written, and also old 
enough for the 550 to be the state of the art rather than just legacy.

  Maciej