RE: [PATCH] cpufreq: imx6q: Fix imx6sx low frequency support

From: Anson Huang
Date: Wed Jul 19 2017 - 21:16:22 EST



Best Regards!
Anson Huang



> -----Original Message-----
> From: Lucas Stach [mailto:l.stach@xxxxxxxxxxxxxx]
> Sent: 2017-07-19 6:28 PM
> To: Leonard Crestez <leonard.crestez@xxxxxxx>
> Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>; Rafael J. Wysocki
> <rjw@xxxxxxxxxxxxx>; Shawn Guo <shawnguo@xxxxxxxxxx>; Fabio Estevam
> <fabio.estevam@xxxxxxx>; linux-pm@xxxxxxxxxxxxxxx; Octavian Purdila
> <octavian.purdila@xxxxxxx>; Anson Huang <anson.huang@xxxxxxx>; Jacky
> Bai <ping.bai@xxxxxxx>; A.s. Dong <aisheng.dong@xxxxxxx>;
> kernel@xxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH] cpufreq: imx6q: Fix imx6sx low frequency support
>
> Hi Leonard,
>
> Am Mittwoch, den 19.07.2017, 12:54 +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 bypassed but still kept enabled.
> > This is required despite the fact that the arm clk is configured to
> > come from
> > pll2_pfd2 and from the clk framework perspective pll1 and related
> > clocks are unused.
>
> I'm not really an expert for MX6SX, so a little background on why PLL1 needs to
> be kept enabled would help to review this change.

Hi, Lucas
The PLL1 needs to be enabled is because 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. This is hardware
requirement.

Anson.

>
> Thanks,
> Lucas
>
> > This patch adds pll1, pll_bypass and pll1_bypass_src clocks to the imx
> > cpufreq driver as imx6sx-specific for the bypass logic.
> >
> > The definition of pll1_sys is changed to imx_clk_fixed_factor so that
> > it's never disabled.
> >
> > Signed-off-by: Leonard Crestez <leonard.crestez@xxxxxxx>
> > ---
> >
> > Some potential issues:
> >
> > In theory pll1_sys could be explictly kept enabled from cpufreq. It's
> > not clear this would be better since the intention is to never let
> > this be disabled.
> >
> > The new clocks are only added for imx6sx. The frequency changing code
> > relies on the fact that the clk API simply does nothing when called
> > with a null clk.
> >
> > Perhaps it might be better to accept ENOENT from clk_get on these new
> > clocks instead of checking of_machine_is_compatible.
> >
> > arch/arm/boot/dts/imx6sx.dtsi | 8 ++++++--
> > drivers/clk/imx/clk-imx6sx.c | 2 +-
> > drivers/cpufreq/imx6q-cpufreq.c | 33
> > +++++++++++++++++++++++++++++++++
> > 3 files changed, 40 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/arm/boot/dts/imx6sx.dtsi
> > b/arch/arm/boot/dts/imx6sx.dtsi index f16b9df..4394137 100644
> > --- a/arch/arm/boot/dts/imx6sx.dtsi
> > +++ b/arch/arm/boot/dts/imx6sx.dtsi
> > @@ -87,9 +87,13 @@
> > <&clks IMX6SX_CLK_PLL2_PFD2>,
> > <&clks IMX6SX_CLK_STEP>,
> > <&clks IMX6SX_CLK_PLL1_SW>,
> > - <&clks IMX6SX_CLK_PLL1_SYS>;
> > + <&clks IMX6SX_CLK_PLL1_SYS>,
> > + <&clks IMX6SX_CLK_PLL1>,
> > + <&clks IMX6SX_PLL1_BYPASS>,
> > + <&clks IMX6SX_PLL1_BYPASS_SRC>;
> > clock-names = "arm", "pll2_pfd2_396m", "step",
> > - "pll1_sw", "pll1_sys";
> > + "pll1_sw", "pll1_sys", "pll1",
> > + "pll1_bypass", "pll1_bypass_src";
> > arm-supply = <&reg_arm>;
> > soc-supply = <&reg_soc>;
> > };
> > diff --git a/drivers/clk/imx/clk-imx6sx.c
> > b/drivers/clk/imx/clk-imx6sx.c index b5c96de..aa63b92 100644
> > --- a/drivers/clk/imx/clk-imx6sx.c
> > +++ b/drivers/clk/imx/clk-imx6sx.c
> > @@ -199,7 +199,7 @@ static void __init imx6sx_clocks_init(struct
> device_node *ccm_node)
> > clk_set_parent(clks[IMX6SX_PLL6_BYPASS], clks[IMX6SX_CLK_PLL6]);
> > clk_set_parent(clks[IMX6SX_PLL7_BYPASS], clks[IMX6SX_CLK_PLL7]);
> >
> > - clks[IMX6SX_CLK_PLL1_SYS] = imx_clk_gate("pll1_sys",
> "pll1_bypass", base + 0x00, 13);
> > + clks[IMX6SX_CLK_PLL1_SYS] = imx_clk_fixed_factor("pll1_sys",
> "pll1_bypass", 1, 1);
> > clks[IMX6SX_CLK_PLL2_BUS] = imx_clk_gate("pll2_bus",
> "pll2_bypass", base + 0x30, 13);
> > clks[IMX6SX_CLK_PLL3_USB_OTG] = imx_clk_gate("pll3_usb_otg",
> "pll3_bypass", base + 0x10, 13);
> > clks[IMX6SX_CLK_PLL4_AUDIO] = imx_clk_gate("pll4_audio",
> "pll4_bypass", base + 0x70, 13);
> > diff --git a/drivers/cpufreq/imx6q-cpufreq.c
> > b/drivers/cpufreq/imx6q-cpufreq.c index b6edd3c..caf727a 100644
> > --- a/drivers/cpufreq/imx6q-cpufreq.c
> > +++ b/drivers/cpufreq/imx6q-cpufreq.c
> > @@ -31,6 +31,9 @@ static struct clk *step_clk; static struct clk
> > *pll2_pfd2_396m_clk;
> >
> > /* clk used by i.MX6UL */
> > +static struct clk *pll1_bypass;
> > +static struct clk *pll1_bypass_src;
> > +static struct clk *pll1;
> > static struct clk *pll2_bus_clk;
> > static struct clk *secondary_sel_clk;
> >
> > @@ -122,8 +125,21 @@ static int imx6q_set_target(struct cpufreq_policy
> *policy, unsigned int index)
> > clk_set_parent(step_clk, pll2_pfd2_396m_clk);
> > clk_set_parent(pll1_sw_clk, step_clk);
> > if (freq_hz > clk_get_rate(pll2_pfd2_396m_clk)) {
> > + /*
> > + * Ensure that pll1_bypass is set back to
> > + * pll1. We have to do this first so that the
> > + * change rate done to pll1_sys_clk done below
> > + * can propagate up to pll1.
> > + */
> > + clk_set_parent(pll1_bypass, pll1);
> > clk_set_rate(pll1_sys_clk, new_freq * 1000);
> > clk_set_parent(pll1_sw_clk, pll1_sys_clk);
> > + } else {
> > + /*
> > + * Need to ensure that PLL1 is bypassed and enabled
> > + * before ARM-PODF is set.
> > + */
> > + clk_set_parent(pll1_bypass, pll1_bypass_src);
> > }
> > }
> >
> > @@ -216,6 +232,17 @@ static int imx6q_cpufreq_probe(struct
> platform_device *pdev)
> > goto put_clk;
> > }
> >
> > + if (of_machine_is_compatible("fsl,imx6sx")) {
> > + pll1 = clk_get(cpu_dev, "pll1");
> > + pll1_bypass = clk_get(cpu_dev, "pll1_bypass");
> > + pll1_bypass_src = clk_get(cpu_dev, "pll1_bypass_src");
> > + if (IS_ERR(pll1) || IS_ERR(pll1_bypass) ||
> IS_ERR(pll1_bypass_src)) {
> > + dev_err(cpu_dev, "failed to get clocks specific to
> imx6sx\n");
> > + ret = -ENOENT;
> > + goto put_clk;
> > + }
> > + }
> > +
> > if (of_machine_is_compatible("fsl,imx6ul") ||
> > of_machine_is_compatible("fsl,imx6ull")) {
> > pll2_bus_clk = clk_get(cpu_dev, "pll2_bus"); @@ -380,6
> +407,12 @@
> > static int imx6q_cpufreq_probe(struct platform_device *pdev)
> > clk_put(step_clk);
> > if (!IS_ERR(pll2_pfd2_396m_clk))
> > clk_put(pll2_pfd2_396m_clk);
> > + if (!IS_ERR(pll1))
> > + clk_put(pll1);
> > + if (!IS_ERR(pll1_bypass))
> > + clk_put(pll1_bypass);
> > + if (!IS_ERR(pll1_bypass_src))
> > + clk_put(pll1_bypass_src);
> > if (!IS_ERR(pll2_bus_clk))
> > clk_put(pll2_bus_clk);
> > if (!IS_ERR(secondary_sel_clk))
>