linux-kernel - Re: [PATCH] serial: atmel: fix incorrect baudrate setup

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Message-ID: <Y7u9SAX++YsXvnVC@kroah.com>
Date:   Mon, 9 Jan 2023 08:07:52 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tobias Schramm <t.schramm@...jaro.org>
Cc:     Richard Genoud <richard.genoud@...il.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: atmel: fix incorrect baudrate setup

On Mon, Jan 09, 2023 at 08:02:00AM +0100, Tobias Schramm wrote:
> Commit ba47f97a18f2 ("serial: core: remove baud_rates when serial console
> setup") changed uart_set_options to select the correct baudrate
> configuration based on the absolute error between requested baudrate and
> available standard baudrate settings.
> Prior to that commit the baudrate was selected based on which predefined
> standard baudrate did not exceed the requested baudrate.
> This change of selection logic was never reflected in the atmel serial
> driver. Thus the comment left in the atmel serial driver is no longer
> accurate.
> Additionally the manual rounding up described in that comment and applied
> via (quot - 1) requests an incorrect baudrate. Since uart_set_options uses
> tty_termios_encode_baud_rate to determine the appropriate baudrate flags
> this can cause baudrate selection to fail entirely because
> tty_termios_encode_baud_rate will only select a baudrate if relative error
> between requested and selected baudrate does not exceed +/-2%.
> Fix that by requesting actual, exact baudrate used by the serial.
> 
> Signed-off-by: Tobias Schramm <t.schramm@...jaro.org>
> ---

What commit id does this fix?  Please list that as a the "Fixes:" tag.

Also, does this need to go to older/stable kernels?

thanks,

greg k-h