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Date: Wed, 26 Jun 2019 10:27:07 +0200
From: Neil Armstrong <narmstrong@...libre.com>
To: Stephen Boyd <sboyd@...nel.org>, jbrunet@...libre.com,
khilman@...libre.com
Cc: linux-arm-kernel@...ts.infradead.org,
linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-clk@...r.kernel.org, martin.blumenstingl@...glemail.com
Subject: Re: [RFC/RFT 07/14] clk: meson: g12a: add notifiers to handle cpu
clock change
On 25/06/2019 22:31, Stephen Boyd wrote:
> 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 <narmstrong@...libre.com>
> [...]
>> @@ -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?
Ack
>
>> + .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?
Would be similar, I'm not against it.
>
>> +}
>> +
>> +struct notifier_block g12a_cpu_clk_mux_nb = {
>
> static?
Ack
>
>> + .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"?
>
Ack
Thanks,
Neil
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