linux-kernel - Re: [PATCH 18/20] tty: n_gsm: fix implicit CR bit encoding in address field

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Date:   Fri, 15 Apr 2022 08:33:32 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "D. Starke" <daniel.starke@...mens.com>
Cc:     linux-serial@...r.kernel.org, jirislaby@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 18/20] tty: n_gsm: fix implicit CR bit encoding in
 address field

On Thu, Apr 14, 2022 at 02:42:23AM -0700, D. Starke wrote:
> From: Daniel Starke <daniel.starke@...mens.com>
> 
> n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010.
> See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1516
> The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to
> the newer 27.010 here. Chapter 5.2.1.2 describes the encoding of the
> address field within the frame header. It is made up of the DLCI address,
> command/response (CR) bit and EA bit.
> Use the predefined CR value instead of a plain 2 in alignment to the
> remaining code and to make the encoding obvious.
> 
> Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
> Cc: stable@...r.kernel.org

This does not change any functionality, so how is this a "fix" or
relevant for stable backporting?


> Signed-off-by: Daniel Starke <daniel.starke@...mens.com>
> ---
>  drivers/tty/n_gsm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index 1e135a71860f..ecd2ecc61b14 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -754,7 +754,7 @@ static void __gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
>  
>  	*--dp = msg->ctrl;
>  	if (gsm->initiator)
> -		*--dp = (msg->addr << 2) | 2 | EA;
> +		*--dp = (msg->addr << 2) | CR | EA;

This is a nice cleanup only.

thanks,

greg k-h