Re: [PATCH] clk: tegra: Fix an infinite loop when clock rate is zero
From: Peter De Schrijver
Date: Mon Sep 24 2018 - 04:06:44 EST
On Fri, Sep 21, 2018 at 06:00:37PM -0400, ryang wrote:
> Calling clk_set_rate or clk_round_rate will lock up the kernel when the
> rate is zero. This avoids the infinite loop and uses a slightly more
> optimized p divider calculation.
>
Acked-By: Peter De Schrijver <pdeschrijver@xxxxxxxxxx>
At some point we should also limit pdiv to its maximum possible value, but
that's not so obvious as we need to take into account PLLs where pdiv is
non-linear.
Peter.
> Signed-off-by: ryang <decatf@xxxxxxxxx>
> ---
> drivers/clk/tegra/clk-pll.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/tegra/clk-pll.c b/drivers/clk/tegra/clk-pll.c
> index 830d1c87fa7c..17a058c3bbc1 100644
> --- a/drivers/clk/tegra/clk-pll.c
> +++ b/drivers/clk/tegra/clk-pll.c
> @@ -582,9 +582,8 @@ static int _calc_rate(struct clk_hw *hw, struct tegra_clk_pll_freq_table *cfg,
> }
>
> /* Raise VCO to guarantee 0.5% accuracy */
> - for (cfg->output_rate = rate; cfg->output_rate < 200 * cfreq;
> - cfg->output_rate <<= 1)
> - p_div++;
> + p_div = rate ? fls((200 * cfreq) / rate) : 0;
> + cfg->output_rate = rate << p_div;
>
> cfg->m = parent_rate / cfreq;
> cfg->n = cfg->output_rate / cfreq;
> --
> 2.17.1
>