linux-kernel - Re: [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation

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Message-ID: <805637056.1640115.1554131118962@webmail.strato.com>
Date:   Mon, 1 Apr 2019 17:05:18 +0200 (CEST)
From:   Ulrich Hecht <uli@...nd.eu>
To:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Ulrich Hecht <uli+renesas@...nd.eu>
Cc:     Eugeniu Rosca <erosca@...adit-jv.com>,
        Dirk Behme <dirk.behme@...bosch.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: sh-sci: Fix HSCIF RX sampling point calculation


> On April 1, 2019 at 1:25 PM Geert Uytterhoeven <geert+renesas@...der.be> wrote:
> 
> 
> There are several issues with the formula used for calculating the
> deviation from the intended rate:
>   1. While min_err and last_stop are signed, srr and baud are unsigned.
>      Hence the signed values are promoted to unsigned, which will lead
>      to a bogus value of deviation if min_err is negative,
>   2. Srr is the register field value, which is one less than the actual
>      sampling rate factor,
>   3. The divisions do not use rounding.
> 
> Fix this by casting unsigned variables to int, adding one to srr, and
> using a single DIV_ROUND_CLOSEST().
> 
> Fixes: 63ba1e00f178a448 ("serial: sh-sci: Support for HSCIF RX sampling point adjustment")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>

Reviewed-by: Ulrich Hecht <uli+renesas@...nd.eu>

CU
Uli