linux-kernel - Re: [PATCH v3 1/8] tty: n_gsm: add restart parameter to DLC specific ioctl config

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Message-ID: <2023042438-whole-cannot-1945@gregkh>
Date:   Mon, 24 Apr 2023 12:54:41 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "D. Starke" <daniel.starke@...mens.com>
Cc:     linux-serial@...r.kernel.org, jirislaby@...nel.org,
        ilpo.jarvinen@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/8] tty: n_gsm: add restart parameter to DLC specific
 ioctl config

On Mon, Apr 24, 2023 at 09:52:44AM +0200, D. Starke wrote:
> From: Daniel Starke <daniel.starke@...mens.com>
> 
> Currently, changing the parameters of a DLCI gives no direct control to the
> user whether this should trigger a channel reset or not. The decision is
> solely made by the driver based on the assumption which parameter changes
> are compatible or not. Therefore, the user has no means to perform an
> automatic channel reset after parameter configuration for non-conflicting
> changes.
> 
> Add the parameter 'restart' to 'gsm_dlci_config' to force a channel reset
> after ioctl setting regardless of whether the changes made require this or
> not.
> 
> Note that the parameter is limited to the values 0 and 1 to allow future
> additions here.
> 
> Signed-off-by: Daniel Starke <daniel.starke@...mens.com>
> ---
>  drivers/tty/n_gsm.c         | 4 ++++
>  include/uapi/linux/gsmmux.h | 3 ++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
> 
> v2 -> v3:
> No changes.
> 
> Link: https://lore.kernel.org/all/20230420085017.7314-2-daniel.starke@siemens.com/
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index b411a26cc092..00f692e2e810 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -2532,6 +2532,8 @@ static int gsm_dlci_config(struct gsm_dlci *dlci, struct gsm_dlci_config *dc, in
>  		return -EINVAL;
>  	if (dc->k > 7)
>  		return -EINVAL;
> +	if (dc->restart > 1)   /* allow future extensions */
> +		return -EINVAL;
>  
>  	/*
>  	 * See what is needed for reconfiguration
> @@ -2546,6 +2548,8 @@ static int gsm_dlci_config(struct gsm_dlci *dlci, struct gsm_dlci_config *dc, in
>  	/* Requires care */
>  	if (dc->priority != dlci->prio)
>  		need_restart = true;
> +	if (dc->restart)
> +		need_restart = true;
>  
>  	if ((open && gsm->wait_config) || need_restart)
>  		need_open = true;
> diff --git a/include/uapi/linux/gsmmux.h b/include/uapi/linux/gsmmux.h
> index eb67884e5f38..33ee7b857c52 100644
> --- a/include/uapi/linux/gsmmux.h
> +++ b/include/uapi/linux/gsmmux.h
> @@ -58,7 +58,8 @@ struct gsm_dlci_config {
>  	__u32 priority;		/* Priority (0 for default value) */
>  	__u32 i;		/* Frame type (1 = UIH, 2 = UI) */
>  	__u32 k;		/* Window size (0 for default value) */
> -	__u32 reserved[8];	/* For future use, must be initialized to zero */
> +	__u32 restart;		/* Force DLCI channel reset? */

Why are you using a full 32 bits for just 1 bit of data here?  Why not
use a bitfield?

And what happened to the request to turn the documentation for this
structure into proper kerneldoc format?

thanks,

greg k-h