linux-kernel - Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

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Date:   Mon, 26 Feb 2018 17:49:22 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Robert Abel <rabel@...ertabel.eu>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Willy Tarreau <w@....eu>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH 3/4] auxdisplay: charlcd: fix x/y address commands

On Mon, Feb 26, 2018 at 12:54 AM, Robert Abel <rabel@...ertabel.eu> wrote:
> NUL-terminate each individual number to be parsed.
> To do this, the next command character and a pointer to its argument
> are found and stored. The command character is then overwritten by NUL
> before kstr* functions are called on the buffer.

It would be useful to have this description in the code itself as a comment.

>
> Signed-off-by: Robert Abel <rabel@...ertabel.eu>
> ---
>  drivers/auxdisplay/charlcd.c | 53 ++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 44 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
> index a3d364e6c666..24cabe88c7f0 100644
> --- a/drivers/auxdisplay/charlcd.c
> +++ b/drivers/auxdisplay/charlcd.c
> @@ -471,28 +471,63 @@ static inline int handle_lcd_special_code(struct charlcd *lcd)
>                 break;
>         }
>         case 'x':       /* gotoxy : LxXXX[yYYY]; */
> -       case 'y':       /* gotoxy : LyYYY[xXXX]; */
> +       case 'y': {     /* gotoxy : LyYYY[xXXX]; */
> +

Extra empty line.

> +               char* nxt_esc;
> +               char  nxt_cmd;

I think skipping the "e" in the names do not buy us much :)

> +               char  cmd;
> +               struct charlcd_priv_addr tmp_addr;
> +
>                 if (!strchr(esc, ';'))
>                         break;
>
> -               while (*esc) {
> -                       if (*esc == 'x') {
> -                               esc++;
> -                               if (kstrtoul(esc, 10, &priv->addr.x) < 0)
> +               /* sequence is processed whether legal or illegal */
> +               processed = 1;
> +
> +               /* copy current address to temporary buffer */
> +               tmp_addr = priv->addr;
> +
> +               nxt_cmd = *esc++;
> +               nxt_esc = esc;
> +
> +               while ('\0' != *esc) {

Please do not change the style of the code w.r.t to the rest of the
file, which writes tests with the non-lvalue on the right-hand side
and do not compare against '\0'. Same for the rest.

> +

Extra empty line.

> +                       cmd = nxt_cmd;
> +                       esc = nxt_esc;
> +                       nxt_esc = strpbrk(esc, "xy;");
> +                       if (NULL != nxt_esc) {
> +                               nxt_cmd = *nxt_esc;
> +                               /* terminate current sequence with NUL */
> +                               *nxt_esc++ = '\0';
> +                       }
> +
> +                       if ('x' == cmd) {
> +                               if (kstrtoul(esc, 10, &tmp_addr.x) < 0)
>                                         break;
> -                       } else if (*esc == 'y') {
> -                               esc++;
> -                               if (kstrtoul(esc, 10, &priv->addr.y) < 0)
> +                       } else if ('y' == cmd) {
> +                               if (kstrtoul(esc, 10, &tmp_addr.y) < 0)
>                                         break;
>                         } else {
> +                               /* break on unknown command or ';' */
>                                 break;
>                         }

{ } not needed (your patch doesn't touch this -- just pointing it out).

> +
>                 }
>
> +               /* unknown commands in sequence will be followed by at least ';' */
> +               if ('\0' != *esc)
> +                       break;
> +
> +               /* clamp new x/y coordinates */
> +               if (tmp_addr.x >= lcd->width)
> +                       tmp_addr.x = lcd->width - 1;

tmp_addr.x = min(tmp_addr.x, lcd->width - 1);

> +               tmp_addr.y %= lcd->height;
> +
> +               priv->addr = tmp_addr;
>                 charlcd_gotoxy(lcd);
> -               processed = 1;
>                 break;
>         }
> +       }

On a general note, the code seems a bit convoluted for what it does,
specially without the comment written in the commit message :-) Isn't
it simpler to use a tiny array in the stack and put the numbers to be
converted instead of modifying the input sequence and dancing with
pointers?

Thanks for the patch!

Cheers,
Miguel

>
>         /* TODO: This indent party here got ugly, clean it! */
>         /* Check whether one flag was changed */
> --
> 2.11.0
>