Re: s3c2410fb: fix clockrate calculation

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 20 Aug 2009 22:50:47 +0100
Ben Dooks <ben@simtec.co.uk> wrote:

> In the final part of the calculation for the tft display clockrate we
> divide the output pf s3c2410fb_calc_pixclk() by 2 which leaves us with
> a rounding error if the result is odd.
> 
> Change to using DIV_ROUND_UP() to ensure that we always choose a higher
> divisor and thus a lower frequency.
> 
> Signed-off-by: Ben Dooks <ben@simtec.co.uk>
> 
> ---
>  drivers/video/s3c2410fb.c |    4 +++-
>  2 files changed, 5 insertions(+), 2 deletions(-)
>  
> Index: b/drivers/video/s3c2410fb.c
> ===================================================================
> --- a/drivers/video/s3c2410fb.c	2009-08-20 08:45:41.000000000 +0100
> +++ b/drivers/video/s3c2410fb.c	2009-08-20 08:45:42.000000000 +0100
> @@ -369,7 +369,9 @@ static void s3c2410fb_activate_var(struc
>  	void __iomem *regs = fbi->io;
>  	int type = fbi->regs.lcdcon1 & S3C2410_LCDCON1_TFT;
>  	struct fb_var_screeninfo *var = &info->var;
> -	int clkdiv = s3c2410fb_calc_pixclk(fbi, var->pixclock) / 2;
> +	int clkdiv;
> +
> +	clkdiv = DIV_ROUND_UP(s3c2410fb_calc_pixclk(fbi, var->pixclock), 2);
>  
>  	printk(KERN_INFO "%s: pixclock=%d, clkdiv=%d\n",
>  	       __func__, var->pixclock, clkdiv);

The changelog forgot to tell us what the impact of this bug is, so I
cannot work out whether we need this fix in 2.6.32, 2.6.31, 2.6.30.x, ....


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