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

[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.

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 at nxp.com>
---

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))
-- 
2.7.4