Re: [PATCH 1/1] tty: n_gsm: Fix SW flow control encoding/handling

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jan 10, 2022 at 11:23:17PM -0800, Daniel Starke wrote:
> According to 3GPP 27.010 chapter 5.2.7.3 DC1 and DC3 (SW flow control)

What is all of that?  Do you have a link to the document that this is
and where it says this?

> are to
> be treated according to ISO/IEC 646.

What is "ISO/IEC 646"?

> That means the MSB shall be ignored.

"MSB"?  Please spell it out, you have plenty of room here.

> This patch applies the needed changes to handle this correctly.

What changes are needed?  Please talk about what you are doing, as the
documentation asks you to so do.

> 
> Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
> ---
>  drivers/tty/n_gsm.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index 0b96b14bbfe1..9ee0643fc9e2 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -322,6 +322,7 @@ static int addr_cnt;
>  #define GSM1_ESCAPE_BITS	0x20
>  #define XON			0x11
>  #define XOFF			0x13
> +#define ASCII_MASK		0x7F

Where did "ASCII" come from?  You didn't say anything about that in the
changelog.

>  static const struct tty_port_operations gsm_port_ops;
>  
> @@ -521,7 +522,7 @@ static void gsm_print_packet(const char *hdr, int addr, int cr,
>   *	@output: output buffer
>   *	@len: length of input
>   *
> - *	Expand a buffer by bytestuffing it. The worst case size change
> + *	Expand a buffer by byte stuffing it. The worst case size change

This change is not described above, and is totally different and belongs
in a different change.


>   *	is doubling and the caller is responsible for handing out
>   *	suitable sized buffers.
>   */
> @@ -531,7 +532,8 @@ static int gsm_stuff_frame(const u8 *input, u8 *output, int len)
>  	int olen = 0;
>  	while (len--) {
>  		if (*input == GSM1_SOF || *input == GSM1_ESCAPE
> -		    || *input == XON || *input == XOFF) {
> +		    || (*input & ASCII_MASK) == XON
> +		    || (*input & ASCII_MASK) == XOFF) {
>  			*output++ = GSM1_ESCAPE;
>  			*output++ = *input++ ^ GSM1_ESCAPE_BITS;
>  			olen++;
> -- 
> 2.25.1
> 

What commit does this fix?

Please read the section entitled "The canonical patch format" in the
kernel file, Documentation/SubmittingPatches for a description of how
to do all of this better.

thanks,

greg k-h