Re: [PATCH] fbdev: omapfb: panel-sony-acx565akm: Simplify show_cabc_available_modes()

[Dan Carpenter <dan.carpenter@linaro.org>]

On Thu, Aug 08, 2024 at 11:46:11AM +0200, Christophe JAILLET wrote:
> Use sysfs_emit_at() instead of snprintf() + custom logic.
> Using sysfs_emit_at() is much more simple.
> 
> Also, sysfs_emit() is already used in this function, so using
> sysfs_emit_at() is more consistent.
> 
> Also simplify the logic:
>   - always add a space after an entry
>   - change the last space into a '\n'
> 
> Finally it is easy to see that, given the size of cabc_modes, PAGE_SIZE
> can not be reached.
> So better keep everything simple (and correct).
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
>  .../omap2/omapfb/displays/panel-sony-acx565akm.c  | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
> index 71d2e015960c..fc975615d5c9 100644
> --- a/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
> +++ b/drivers/video/fbdev/omap2/omapfb/displays/panel-sony-acx565akm.c
> @@ -466,19 +466,20 @@ static ssize_t show_cabc_available_modes(struct device *dev,
>  		char *buf)
>  {
>  	struct panel_drv_data *ddata = dev_get_drvdata(dev);
> -	int len;
> +	int len = 0;
>  	int i;
>  
>  	if (!ddata->has_cabc)
>  		return sysfs_emit(buf, "%s\n", cabc_modes[0]);
>  
> -	for (i = 0, len = 0;
> -	     len < PAGE_SIZE && i < ARRAY_SIZE(cabc_modes); i++)
> -		len += snprintf(&buf[len], PAGE_SIZE - len, "%s%s%s",
> -			i ? " " : "", cabc_modes[i],
> -			i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");
> +	for (i = 0; i < ARRAY_SIZE(cabc_modes); i++)
> +		len += sysfs_emit_at(buf, len, "%s ", cabc_modes[i]);
> +
> +	/* Remove the trailing space */
> +	if (len)
> +		buf[len - 1] = '\n';

I'm uncomfortable with this line.  It assumes we don't overflow PAGE_SIZE where
the original code was careful about checking.  Probably easiest to do what the
original code did and say:

	for (i = 0; i < ARRAY_SIZE(cabc_modes); i++)
		len += sysfs_emit_at(buf, len, "%s%s", cabc_modes[i],
				     i == ARRAY_SIZE(cabc_modes) - 1 ? "\n" : "");

regards,
dan carpenter