Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S932749AbeAKNTt (ORCPT <rfc822;ralf@linux-mips.org> + 1 other);
        Thu, 11 Jan 2018 08:19:49 -0500
Received: from mail.linuxfoundation.org ([140.211.169.12]:48014 "EHLO
        mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S932534AbeAKNTr (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 11 Jan 2018 08:19:47 -0500
Date: Thu, 11 Jan 2018 14:19:47 +0100
From: Greg KH <gregkh@linuxfoundation.org>
To: Nuno =?iso-8859-1?Q?Gon=E7alves?= <nunojpg@gmail.com>
Cc: ed.blake@sondrel.com, linux-kernel@vger.kernel.org
Subject: Re: 8250_dw bug
Message-ID: <20180111131947.GA16628@kroah.com>
References: <CAEXMXLR=wuxgPJHGmn0bTUC5_8kZ-mc1u3FmAGyAs9HmV_FNig@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <CAEXMXLR=wuxgPJHGmn0bTUC5_8kZ-mc1u3FmAGyAs9HmV_FNig@mail.gmail.com>
User-Agent: Mutt/1.9.2 (2017-12-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

On Thu, Jan 11, 2018 at 01:47:31PM +0100, Nuno Gon?alves wrote:
> Dear Ed and Greg,
> 
> There is a small bug on de9e33bdfa22e607a88494ff21e9196d00bf4550, at
> least on 32bit devices.
> 
> Line 274 if (rate >= i * min_rate && rate <= i * max_rate)
> 
> This will overflow when min_rate/max_rate is large and can not be
> achieved in the hardware.
> 
> Eg.
> 
> stty -F /dev/ttyS2 raw 3500000 (not achievable on my board).
> 
> target_rate=56000000 (for 3500000baud)
> min_rate=55125000
> max_rate=56875000
> rate=24000000 (clk_round_rate for my board)
> 
> Since my board can only do 1500000baud, this loop will keep
> incrementing i until i=77*56875000 will overflow, and there are
> unexpected results.
> 
> I suggest this patch:
> 
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -267,7 +267,13 @@ static void dw8250_set_termios(struct uart_port
> *p, struct ktermios *termios,
> 
>         for (i = 1; i <= UART_DIV_MAX; i++) {
>                 rate = clk_round_rate(d->clk, i * target_rate);
> -               if (rate >= i * min_rate && rate <= i * max_rate)
> +
> +               if (rate < i * min_rate) {
> +                       i = UART_DIV_MAX;
> +                       break;
> +               }
> +
> +               if (rate <= i * max_rate)
>                         break;
>         }
>         if (i <= UART_DIV_MAX) {
> 
> 
> Let me know if you want me to submit the formal patch.

Why wouldn't you submit a "formal patch", that way we could apply it if
it is correct :)

also cc: the linux-serial mailing list when you do so, thanks.

greg k-h