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

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Date:   Mon, 26 Feb 2018 17:57:15 +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 5:49 PM, Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
> 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).

Disregard this one, just checked and coding-style.rst specifies one
must use braces if the other branches need to use them.

Cheers,
Miguel

>
>> +
>>                 }
>>
>> +               /* 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
>>