linux-kernel - Re: [PATCH] tty: n_gsm: Fix CR bit value when initiator=0

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Date:   Wed, 16 Jun 2021 08:19:59 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Zhenguo Zhao <zhenguo6858@...il.com>
Cc:     jirislaby@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH]    tty: n_gsm: Fix CR bit value when initiator=0

On Wed, Jun 16, 2021 at 10:56:39AM +0800, Zhenguo Zhao wrote:
> From: Zhenguo Zhao <zhenguo.zhao1@...soc.com>
> 
> 	When set initiator=0,switch to Responder,gsmld received dlci SABM/DISC
> 	frame,CR bit should be 0 by calculation.
> 
> 	receive DLC0 SABM CMD:
> 	[69.740263] c1 gsmld_receive: 00000000: f9 03 3f 01 1c f9
> 	[69.893247] c1 gsm_queue cr:1
> 	[69.897629] c1 <-- 0) C: SABM(P)
> 	[69.907516] c1 gsm_queue cr:0

Why is this changelog text indented by tabs?

And I do not understand the changelog text here, what is this showing?
What is wrong here and what is being fixed?

> Signed-off-by: Zhenguo Zhao <zhenguo.zhao1@...soc.com>

Does this fix a long-standing issue?  Should a "Fixes:" tag go here?  If
so, please provide it.

Should it also be sent to stable kernels?

> ---
>  drivers/tty/n_gsm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index 5fea02c..becca2c 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -1779,7 +1779,7 @@ static void gsm_queue(struct gsm_mux *gsm)
>  
>  	switch (gsm->control) {
>  	case SABM|PF:
> -		if (cr == 0)
> +		if (cr == 1)

How did the original code ever work properly?

>  			goto invalid;
>  		if (dlci == NULL)
>  			dlci = gsm_dlci_alloc(gsm, address);
> @@ -1793,7 +1793,7 @@ static void gsm_queue(struct gsm_mux *gsm)
>  		}
>  		break;
>  	case DISC|PF:
> -		if (cr == 0)
> +		if (cr == 1)

Same here, how did this ever work?  Are you sure this change is correct?

thanks,

greg k-h