linux-kernel - Re: [PATCH v3 2/2] auxdisplay: charlcd: Deduplicate simple

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Date:   Mon, 8 Jul 2019 15:16:52 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Miguel Ojeda Sandonis <miguel.ojeda.sandonis@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mans Rullgard <mans@...sr.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] auxdisplay: charlcd: Deduplicate simple_strtoul()

On Thu 2019-07-04 14:55:32, Andy Shevchenko wrote:
> Like in the commit
>   8b2303de399f ("serial: core: Fix handling of options after MMIO address")
> we may use simple_strtoul() which in comparison to kstrtoul() can do conversion
> in-place without additional and unnecessary code to be written.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> - no change since v2
>  drivers/auxdisplay/charlcd.c | 34 +++++++---------------------------
>  1 file changed, 7 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
> index 92745efefb54..3858dc7a4154 100644
> --- a/drivers/auxdisplay/charlcd.c
> +++ b/drivers/auxdisplay/charlcd.c
> @@ -287,31 +287,6 @@ static int charlcd_init_display(struct charlcd *lcd)
>  	return 0;
>  }
>  
> -/*
> - * Parses an unsigned integer from a string, until a non-digit character
> - * is found. The empty string is not accepted. No overflow checks are done.
> - *
> - * Returns whether the parsing was successful. Only in that case
> - * the output parameters are written to.
> - *
> - * TODO: If the kernel adds an inplace version of kstrtoul(), this function
> - * could be easily replaced by that.
> - */
> -static bool parse_n(const char *s, unsigned long *res, const char **next_s)
> -{
> -	if (!isdigit(*s))
> -		return false;
> -
> -	*res = 0;
> -	while (isdigit(*s)) {
> -		*res = *res * 10 + (*s - '0');
> -		++s;
> -	}
> -
> -	*next_s = s;
> -	return true;
> -}
> -
>  /*
>   * Parses a movement command of the form "(.*);", where the group can be
>   * any number of subcommands of the form "(x|y)[0-9]+".
> @@ -336,6 +311,7 @@ static bool parse_xy(const char *s, unsigned long *x, unsigned long *y)
>  {
>  	unsigned long new_x = *x;
>  	unsigned long new_y = *y;
> +	char *p;
>  
>  	for (;;) {
>  		if (!*s)
> @@ -345,11 +321,15 @@ static bool parse_xy(const char *s, unsigned long *x, unsigned long *y)
>  			break;
>  
>  		if (*s == 'x') {
> -			if (!parse_n(s + 1, &new_x, &s))
> +			new_x = simple_strtoul(s + 1, &p, 10);

simple_strtoul() tries to detect the base even when it has been
explicitely specified. I am afraid that it might cause some
regressions.

For example, the following input is strange but it is valid:

    x0x10;  new code would return (16, <orig_y>) instead of (10, <orig_y>)
    x010;   new code would return (8, <orig_y>) instead of (10, <orig_y>)

Best Regards,
Petr