Re: [PATCH] staging: sm750fb: refactor the clock frequency calculation method
From: Greg KH
Date: Mon Jul 03 2017 - 02:21:59 EST
On Sun, Jul 02, 2017 at 08:24:26PM +0800, Lynn Lei wrote:
> speed up calculation by merging two divisions into one.
How much did you speed it up? Please provide proof of anything like
this if you say it is a speed up.
> Signed-off-by: Lynn Lei <lynnl.wit@xxxxxxxxx>
> drivers/staging/sm750fb/ddk750_chip.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> diff --git a/drivers/staging/sm750fb/ddk750_chip.c b/drivers/staging/sm750fb/ddk750_chip.c
> index c51761221131..5970c3792f27 100644
> --- a/drivers/staging/sm750fb/ddk750_chip.c
> +++ b/drivers/staging/sm750fb/ddk750_chip.c
> @@ -44,7 +44,7 @@ static unsigned int get_mxclk_freq(void)
> OD = (pll_reg & PLL_CTRL_OD_MASK) >> PLL_CTRL_OD_SHIFT;
> POD = (pll_reg & PLL_CTRL_POD_MASK) >> PLL_CTRL_POD_SHIFT;
> - return DEFAULT_INPUT_CLOCK * M / N / (1 << OD) / (1 << POD);
> + return DEFAULT_INPUT_CLOCK * M / N / (1 << (OD + POD));
Are you sure that gcc didn't already do this for you? It's a constant
number, I doubt this did anything at all.