linux-kernel - Re: [PATCHv2 3/4] tty: n_gsm: add helper to convert mux-num to/from tty-base

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Date:   Wed, 10 Jul 2019 12:48:32 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Martin Hundebøll <martin@...nix.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
        Sean Nyekjær <sean@...nix.com>,
        Esben Haabendal <esben@...nix.com>
Subject: Re: [PATCHv2 3/4] tty: n_gsm: add helper to convert mux-num to/from
 tty-base

On Tue,  9 Jul 2019 08:46:32 +0200
Martin Hundebøll <martin@...nix.com> wrote:

> Make it obvious how the gsm mux number relates to the virtual tty lines
> by using helper function instead of shifting 6 bits.
> 
> Signed-off-by: Martin Hundebøll <martin@...nix.com>
> ---
>  drivers/tty/n_gsm.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
> index c4e16b31f9ab..cba06063c44a 100644
> --- a/drivers/tty/n_gsm.c
> +++ b/drivers/tty/n_gsm.c
> @@ -2171,6 +2171,16 @@ static inline void mux_put(struct gsm_mux *gsm)
>  	kref_put(&gsm->ref, gsm_free_muxr);
>  }
>  
> +static inline int mux_num_to_base(struct gsm_mux *gsm)
> +{
> +	return gsm->num * NUM_DLCI;
> +}
> +
> +static inline unsigned int mux_line_to_num(int line)
> +{
> +	return line / NUM_DLCI;

If you are going to convert shifts to multiply and divide then used
unsigned maths so the compiler can optimize it nicely on some of the low
end processors.

Alan