Re: [PATCH] cpufreq: imx6q: Fix imx6sx low frequency support
From: Lucas Stach
Date: Mon Aug 28 2017 - 08:08:04 EST
Am Montag, den 28.08.2017, 14:05 +0300 schrieb Leonard Crestez:
> This patch contains the minimal changes required to support imx6sx OPP
> of 198 Mhz. Without this patch cpufreq still reports success but the
> frequency is not changed, the "arm" clock will still be at 396000000 in
> clk_summary.
>
> In order to do this PLL1 needs to be still kept enabled while changing
> the ARM clock. This is a hardware requirement: when ARM_PODF is changed
> in CCM we need to check the busy bit of CCM_CDHIPR bit 16 arm_podf_busy,
> and this bit is sync with PLL1 clock, so if PLL1 NOT enabled, this
> bit will never get clear.
>
> Keep pll1_sys explicitly enabled until after the rate is change to deal
> with this. Otherwise from the clk framework perspective pll1_sys is
> unused and gets turned off.
>
> Signed-off-by: Leonard Crestez <leonard.crestez@xxxxxxx>
Reviewed-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> ---
> Changes since v1:
> - Link: https://lkml.org/lkml/2017/7/19/302
> - Only keep pll1_sys enabled until after ARM rate is changed.
> - Incorporate more elaborate explanation from Anson
> - Do not add new clocks or bypass PLL1. Just let it get disabled.
>
> drivers/cpufreq/imx6q-cpufreq.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/cpufreq/imx6q-cpufreq.c b/drivers/cpufreq/imx6q-cpufreq.c
> index b6edd3c..14466a9 100644
> --- a/drivers/cpufreq/imx6q-cpufreq.c
> +++ b/drivers/cpufreq/imx6q-cpufreq.c
> @@ -47,6 +47,7 @@ static int imx6q_set_target(struct cpufreq_policy *policy, unsigned int index)
> struct dev_pm_opp *opp;
> unsigned long freq_hz, volt, volt_old;
> unsigned int old_freq, new_freq;
> + bool pll1_sys_temp_enabled = false;
> int ret;
>
> new_freq = freq_table[index].frequency;
> @@ -124,6 +125,10 @@ static int imx6q_set_target(struct cpufreq_policy *policy, unsigned int index)
> if (freq_hz > clk_get_rate(pll2_pfd2_396m_clk)) {
> clk_set_rate(pll1_sys_clk, new_freq * 1000);
> clk_set_parent(pll1_sw_clk, pll1_sys_clk);
> + } else {
> + /* pll1_sys needs to be enabled for divider rate change to work. */
> + pll1_sys_temp_enabled = true;
> + clk_prepare_enable(pll1_sys_clk);
> }
> }
>
> @@ -135,6 +140,10 @@ static int imx6q_set_target(struct cpufreq_policy *policy, unsigned int index)
> return ret;
> }
>
> + /* PLL1 is only needed until after ARM-PODF is set. */
> + if (pll1_sys_temp_enabled)
> + clk_disable_unprepare(pll1_sys_clk);
> +
> /* scaling down? scale voltage after frequency */
> if (new_freq < old_freq) {
> ret = regulator_set_voltage_tol(arm_reg, volt, 0);