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SubjectRe: [PATCH v2 01/16] clk: sunxi-ng: Add check for minimal rate to NM PLLs
Hi,

On Tue, Feb 27, 2018 at 11:26:46PM +0100, Jernej Skrabec wrote:
> Some NM PLLs doesn't work well when their output clock rate is set below
> certain rate.
>
> Add support for that constrain.
>
> Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> ---
> drivers/clk/sunxi-ng/ccu_nm.c | 11 +++++++----
> drivers/clk/sunxi-ng/ccu_nm.h | 27 +++++++++++++++++++++++++++
> 2 files changed, 34 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/clk/sunxi-ng/ccu_nm.c b/drivers/clk/sunxi-ng/ccu_nm.c
> index a16de092bf94..7fc743c78c1b 100644
> --- a/drivers/clk/sunxi-ng/ccu_nm.c
> +++ b/drivers/clk/sunxi-ng/ccu_nm.c
> @@ -20,7 +20,7 @@ struct _ccu_nm {
> };
>
> static void ccu_nm_find_best(unsigned long parent, unsigned long rate,
> - struct _ccu_nm *nm)
> + unsigned long min_rate, struct _ccu_nm *nm)
> {
> unsigned long best_rate = 0;
> unsigned long best_n = 0, best_m = 0;
> @@ -30,7 +30,7 @@ static void ccu_nm_find_best(unsigned long parent, unsigned long rate,
> for (_m = nm->min_m; _m <= nm->max_m; _m++) {
> unsigned long tmp_rate = parent * _n / _m;
>
> - if (tmp_rate > rate)
> + if (tmp_rate > rate || tmp_rate < min_rate)
> continue;
>
> if ((rate - tmp_rate) < (rate - best_rate)) {
> @@ -117,6 +117,9 @@ static long ccu_nm_round_rate(struct clk_hw *hw, unsigned long rate,
> if (nm->common.features & CCU_FEATURE_FIXED_POSTDIV)
> rate *= nm->fixed_post_div;
>
> + if (rate < nm->min_rate)
> + rate = nm->min_rate;
> +

I guess you can just return there. There's no point in trying to find
the factors at this point, since the minimum should be a value that
can be reached.

> if (ccu_frac_helper_has_rate(&nm->common, &nm->frac, rate)) {
> if (nm->common.features & CCU_FEATURE_FIXED_POSTDIV)
> rate /= nm->fixed_post_div;
> @@ -134,7 +137,7 @@ static long ccu_nm_round_rate(struct clk_hw *hw, unsigned long rate,
> _nm.min_m = 1;
> _nm.max_m = nm->m.max ?: 1 << nm->m.width;
>
> - ccu_nm_find_best(*parent_rate, rate, &_nm);
> + ccu_nm_find_best(*parent_rate, rate, nm->min_rate, &_nm);

Therefore, you don't need to change the prototype there either.

Maxime

--
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com
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