[PATCH 02/20] clk: multiplier: Prevent the multiplier from under / over flowing

[Michael Turquette]

Quoting Maxime Ripard (2016-05-16 05:47:02)
> In the current multiplier base clock implementation, if the
> CLK_SET_RATE_PARENT flag isn't set, the code will not make sure that the
> multiplier computed remains within the boundaries of our clock.
> 
> This means that if the clock we want to reach is below the parent rate,
> or if the multiplier is above the maximum that we can reach, we will end up
> with a completely bogus one that the clock cannot achieve.
> 
> Fixes: f2e0a53271a4 ("clk: Add a basic multiplier clock")
> Signed-off-by: Maxime Ripard <maxime.ripard at free-electrons.com>

Applied.

Regards,
Mike

> ---
>  drivers/clk/clk-multiplier.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clk/clk-multiplier.c b/drivers/clk/clk-multiplier.c
> index 9e449c7b751c..dc037c957acd 100644
> --- a/drivers/clk/clk-multiplier.c
> +++ b/drivers/clk/clk-multiplier.c
> @@ -52,14 +52,28 @@ static unsigned long __bestmult(struct clk_hw *hw, unsigned long rate,
>                                 unsigned long *best_parent_rate,
>                                 u8 width, unsigned long flags)
>  {
> +       struct clk_multiplier *mult = to_clk_multiplier(hw);
>         unsigned long orig_parent_rate = *best_parent_rate;
>         unsigned long parent_rate, current_rate, best_rate = ~0;
>         unsigned int i, bestmult = 0;
> +       unsigned int maxmult = (1 << width) - 1;
> +
> +       if (!(clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT)) {
> +               bestmult = rate / orig_parent_rate;
> +
> +               /* Make sure we don't end up with a 0 multiplier */
> +               if ((bestmult == 0) &&
> +                   !(mult->flags & CLK_MULTIPLIER_ZERO_BYPASS))
> +                       bestmult = 1;
>  
> -       if (!(clk_hw_get_flags(hw) & CLK_SET_RATE_PARENT))
> -               return rate / *best_parent_rate;
> +               /* Make sure we don't overflow the multiplier */
> +               if (bestmult > maxmult)
> +                       bestmult = maxmult;
> +
> +               return bestmult;
> +       }
>  
> -       for (i = 1; i < ((1 << width) - 1); i++) {
> +       for (i = 1; i < maxmult; i++) {
>                 if (rate == orig_parent_rate * i) {
>                         /*
>                          * This is the best case for us if we have a
> -- 
> 2.8.2
>