Subject: Re: [RFC/RFT 07/14] clk: meson: g12a: add notifiers to handle cpu clock change

From: Stephen Boyd <[email-masked]>
Date: Tue, 25 Jun 2019 13:31:51 -0700

Quoting Neil Armstrong (2019-06-20 08:00:06)
> In order to implement clock switching for the CLKID_CPU_CLK and
> CLKID_CPUB_CLK, notifiers are added on specific points of the
> clock tree :
> 
> cpu_clk / cpub_clk
> |   \- cpu_clk_dyn
> |      |  \- cpu_clk_premux0
> |      |        |- cpu_clk_postmux0
> |      |        |    |- cpu_clk_dyn0_div
> |      |        |    \- xtal/fclk_div2/fclk_div3
> |      |        \- xtal/fclk_div2/fclk_div3
> |      \- cpu_clk_premux1
> |            |- cpu_clk_postmux1
> |            |    |- cpu_clk_dyn1_div
> |            |    \- xtal/fclk_div2/fclk_div3
> |            \- xtal/fclk_div2/fclk_div3
> \ sys_pll / sys1_pll
> 
> This for each cluster, a single one for G12A, two for G12B.
> 
> Each cpu_clk_premux1 tree is marked as read-only and CLK_SET_RATE_NO_REPARENT,
> to be used as "parking" clock in a safe clock frequency.
> 
> A notifier is added on each cpu_clk_premux0 to detech when CCF want to
> change the frequency of the cpu_clk_dyn tree.
> In this notifier, the cpu_clk_premux1 tree is configured to use the xtal
> clock and then the cpu_clk_dyn is switch to cpu_clk_premux1 while CCF
> updates the cpu_clk_premux0 tree.
> 
> A notifier is added on each sys_pll/sys1_pll to detect when CCF wants to
> change the PLL clock source of the cpu_clk.
> In this notifier, the cpu_clk is switched to cpu_clk_dyn while CCF
> updates the sys_pll/sys1_pll frequency.
> 
> A third small notifier is added on each cpu_clk / cpub_clk and cpu_clk_dyn,
> add a small delay at PRE_RATE_CHANGE/POST_RATE_CHANGE to let the other
> notofiers change propagate before changing the cpu_clk_premux0 and sys_pll
> clock trees.
> 
> This notifier set permits switching the cpu_clk / cpub_clk without any
> glitches and using a safe parking clock while switching between sub-GHz
> clocks using the cpu_clk_dyn tree.
> 
> This setup has been tested and validated on the Amlogic G12A and G12B
> SoCs running the arm64 cpuburn at [1] and cycling between all the possible
> cpufreq translations of each cluster and checking the final frequency using
> the clock-measurer, script at [2].
> 
> [1] https://github.com/ssvb/cpuburn-arm/blob/master/cpuburn-a53.S
> [2] https://gist.github.com/superna9999/d4de964dbc0f84b7d527e1df2ddea25f
> 
> Signed-off-by: Neil Armstrong <[email-masked]>
[...]
> @@ -418,6 +458,35 @@ static struct clk_regmap g12b_cpub_clk_premux0 = {
>         },
>  };
>  
> +/* This divider uses bit 26 to take change in account */
> +static int g12b_cpub_clk_mux0_div_set_rate(struct clk_hw *hw, unsigned long rate,
> +                                         unsigned long parent_rate)
> +{
> +       struct clk_regmap *clk = to_clk_regmap(hw);
> +       struct clk_regmap_div_data *div = clk_get_regmap_div_data(clk);
> +       unsigned int val;
> +       int ret;
> +
> +       ret = divider_get_val(rate, parent_rate, div->table, div->width,
> +                             div->flags);
> +       if (ret < 0)
> +               return ret;
> +
> +       val = (unsigned int)ret << div->shift;
> +
> +       regmap_update_bits(clk->map, HHI_SYS_CPUB_CLK_CNTL,
> +                          SYS_CPU_DYN_ENABLE, SYS_CPU_DYN_ENABLE);
> +
> +       return regmap_update_bits(clk->map, div->offset,
> +                                 clk_div_mask(div->width) << div->shift | SYS_CPU_DYN_ENABLE, val);
> +};
> +
> +const struct clk_ops g12b_cpub_clk_mux0_div_ops = {

static?

> +       .recalc_rate = clk_regmap_div_recalc_rate,
> +       .round_rate = clk_regmap_div_round_rate,
> +       .set_rate = g12b_cpub_clk_mux0_div_set_rate,
> +};
> +
>  /* Datasheet names this field as "mux0_divn_tcnt" */
>  static struct clk_regmap g12b_cpub_clk_mux0_div = {
>         .data = &(struct clk_regmap_div_data){
[...]
>  
> +static int g12a_cpu_clk_mux_notifier_cb(struct notifier_block *nb,
> +                                       unsigned long event, void *data)
> +{
> +       switch (event) {
> +       case POST_RATE_CHANGE:
> +       case PRE_RATE_CHANGE:
> +               /* Wait for clock propagation before/after changing the mux */
> +               udelay(100);
> +               return NOTIFY_OK;
> +
> +       default:
> +               return NOTIFY_DONE;
> +       }

Maybe convert this into a if statement and then have a default return
of NOTIFY_DONE otherwise?

> +}
> +
> +struct notifier_block g12a_cpu_clk_mux_nb = {

static?

> +       .notifier_call = g12a_cpu_clk_mux_notifier_cb,
> +};
> +
> +struct g12a_cpu_clk_postmux_nb_data {
> +       struct notifier_block nb;
> +       struct clk_hw *xtal;
> +       struct clk_hw *cpu_clk_dyn;
> +       struct clk_hw *cpu_clk_postmux0;
> +       struct clk_hw *cpu_clk_postmux1;
> +       struct clk_hw *cpu_clk_premux1;
> +};
> +
> +static int g12a_cpu_clk_postmux_notifier_cb(struct notifier_block *nb,
> +                                        unsigned long event, void *data)
> +{
> +       struct g12a_cpu_clk_postmux_nb_data *nb_data =
> +               container_of(nb, struct g12a_cpu_clk_postmux_nb_data, nb);
> +
> +       switch (event) {
> +       case PRE_RATE_CHANGE:
> +               /*
> +                * This notifier means cpu_clk_postmux0 clock will be changed
> +                * to feed cpu_clk, this the current path :

Maybe write "this is the current path"?

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