ARM: imx: avoid calling clk APIs in idle thread which may cause schedule

As clk_pllv3_wait_lock will call usleep_range, and the clk APIs
mutex lock may be held when CPU entering idle, so calling clk
APIs must be avoided in cpu idle thread, this is to avoid reschedule
warning in cpu idle, just access register directly to achieve that.

bad: scheduling from the idle thread!
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.14.0-rc1+ #657
Backtrace:
[<80012188>] (dump_backtrace) from [<8001246c>] (show_stack+0x18/0x1c)
 r6:808c0038 r5:00000000 r4:808e5a1c r3:00000000
[<80012454>] (show_stack) from [<8064b2ec>] (dump_stack+0x84/0x9c)
[<8064b268>] (dump_stack) from [<80055ee0>] (dequeue_task_idle+0x20/0x30)
 r5:808bef40 r4:bf7dff40
[<80055ec0>] (dequeue_task_idle) from [<8004f028>] (dequeue_task+0x30/0x50)
 r4:bf7dff40 r3:80055ec0
[<8004eff8>] (dequeue_task) from [<800503c0>] (deactivate_task+0x30/0x34)
 r4:bf7dff40
[<80050390>] (deactivate_task) from [<8064d8e4>] (__schedule+0x2c8/0x5c0)
[<8064d61c>] (__schedule) from [<8064dc14>] (schedule+0x38/0x88)
 r10:80912964 r9:808c1e50 r8:808c0038 r7:808cbf30 r6:80e128ec r5:60000093
 r4:80912968
[<8064dbdc>] (schedule) from [<8064dfec>] (schedule_preempt_disabled+0x10/0x14)
[<8064dfdc>] (schedule_preempt_disabled) from [<8064ebc0>] (mutex_lock_nested+0x1c0/0x3c0)
[<8064ea00>] (mutex_lock_nested) from [<804ae71c>] (clk_prepare_lock+0x44/0xe4)
 r10:806554cc r9:bf7df1bc r8:808cf4f8 r7:808cf544 r6:bf7df1b8 r5:808c0010
 r4:80e69750
[<804ae6d8>] (clk_prepare_lock) from [<804af214>] (clk_get_rate+0x14/0x64)
 r6:bf7df1b8 r5:00000002 r4:bf017000 r3:80922ad0
[<804af200>] (clk_get_rate) from [<80025d30>] (imx6sl_set_wait_clk+0x18/0x20)
 r5:00000002 r4:00000001
[<80025d18>] (imx6sl_set_wait_clk) from [<80023454>] (imx6sl_enter_wait+0x20/0x48)
[<80023434>] (imx6sl_enter_wait) from [<80477c24>] (cpuidle_enter_state+0x44/0xfc)
 r4:3c386e48 r3:80023434
[<80477be0>] (cpuidle_enter_state) from [<80477dd8>] (cpuidle_idle_call+0xfc/0x160)
 r8:808cf4f8 r7:00000001 r6:80e69534 r5:00000000 r4:bf7df1b8
[<80477cdc>] (cpuidle_idle_call) from [<8000f61c>] (arch_cpu_idle+0x10/0x50)
 r9:808c0000 r8:00000000 r7:80921a89 r6:808c8938 r5:808c899c r4:808c0000
[<8000f60c>] (arch_cpu_idle) from [<8006fa94>] (cpu_startup_entry+0x108/0x160)
[<8006f98c>] (cpu_startup_entry) from [<806452ac>] (rest_init+0xb4/0xdc)
 r7:808afae0
[<806451f8>] (rest_init) from [<8086fb58>] (start_kernel+0x328/0x38c)
 r6:ffffffff r5:808c8880 r4:808c8a30
[<8086f830>] (start_kernel) from [<80008074>] (0x80008074)
Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/clk-imx6sl.c

@@ -18,6 +18,22 @@
 #include "clk.h"
 #include "common.h"
 
+#define CCSR			0xc
+#define BM_CCSR_PLL1_SW_CLK_SEL	(1 << 2)
+#define CACRR			0x10
+#define CDHIPR			0x48
+#define BM_CDHIPR_ARM_PODF_BUSY	(1 << 16)
+#define ARM_WAIT_DIV_396M	2
+#define ARM_WAIT_DIV_792M	4
+#define ARM_WAIT_DIV_996M	6
+
+#define PLL_ARM			0x0
+#define BM_PLL_ARM_DIV_SELECT	(0x7f << 0)
+#define BM_PLL_ARM_POWERDOWN	(1 << 12)
+#define BM_PLL_ARM_ENABLE	(1 << 13)
+#define BM_PLL_ARM_LOCK		(1 << 31)
+#define PLL_ARM_DIV_792M	66
+
 static const char *step_sels[]		= { "osc", "pll2_pfd2", };
 static const char *pll1_sw_sels[]	= { "pll1_sys", "step", };
 static const char *ocram_alt_sels[]	= { "pll2_pfd2", "pll3_pfd1", };
@@ -65,6 +81,8 @@ static struct clk_div_table video_div_table[] = {
 
 static struct clk *clks[IMX6SL_CLK_END];
 static struct clk_onecell_data clk_data;
+static void __iomem *ccm_base;
+static void __iomem *anatop_base;
 
 static const u32 clks_init_on[] __initconst = {
 	IMX6SL_CLK_IPG, IMX6SL_CLK_ARM, IMX6SL_CLK_MMDC_ROOT,
@@ -81,19 +99,70 @@ static const u32 clks_init_on[] __initconst = {
  * entering WAIT mode.
  *
  * This function will set the ARM clk to max value within the 12:5 limit.
+ * As IPG clock is fixed at 66MHz(so ARM freq must not exceed 158.4MHz),
+ * ARM freq are one of below setpoints: 396MHz, 792MHz and 996MHz, since
+ * the clk APIs can NOT be called in idle thread(may cause kernel schedule
+ * as there is sleep function in PLL wait function), so here we just slow
+ * down ARM to below freq according to previous freq:
+ *
+ * run mode      wait mode
+ * 396MHz   ->   132MHz;
+ * 792MHz   ->   158.4MHz;
+ * 996MHz   ->   142.3MHz;
  */
+static int imx6sl_get_arm_divider_for_wait(void)
+{
+	if (readl_relaxed(ccm_base + CCSR) & BM_CCSR_PLL1_SW_CLK_SEL) {
+		return ARM_WAIT_DIV_396M;
+	} else {
+		if ((readl_relaxed(anatop_base + PLL_ARM) &
+			BM_PLL_ARM_DIV_SELECT) == PLL_ARM_DIV_792M)
+			return ARM_WAIT_DIV_792M;
+		else
+			return ARM_WAIT_DIV_996M;
+	}
+}
+
+static void imx6sl_enable_pll_arm(bool enable)
+{
+	static u32 saved_pll_arm;
+	u32 val;
+
+	if (enable) {
+		saved_pll_arm = val = readl_relaxed(anatop_base + PLL_ARM);
+		val |= BM_PLL_ARM_ENABLE;
+		val &= ~BM_PLL_ARM_POWERDOWN;
+		writel_relaxed(val, anatop_base + PLL_ARM);
+		while (!(__raw_readl(anatop_base + PLL_ARM) & BM_PLL_ARM_LOCK))
+			;
+	} else {
+		 writel_relaxed(saved_pll_arm, anatop_base + PLL_ARM);
+	}
+}
+
 void imx6sl_set_wait_clk(bool enter)
 {
-	static unsigned long saved_arm_rate;
+	static unsigned long saved_arm_div;
+	int arm_div_for_wait = imx6sl_get_arm_divider_for_wait();
+
+	/*
+	 * According to hardware design, arm podf change need
+	 * PLL1 clock enabled.
+	 */
+	if (arm_div_for_wait == ARM_WAIT_DIV_396M)
+		imx6sl_enable_pll_arm(true);
 
 	if (enter) {
-		unsigned long ipg_rate = clk_get_rate(clks[IMX6SL_CLK_IPG]);
-		unsigned long max_arm_wait_rate = (12 * ipg_rate) / 5;
-		saved_arm_rate = clk_get_rate(clks[IMX6SL_CLK_ARM]);
-		clk_set_rate(clks[IMX6SL_CLK_ARM], max_arm_wait_rate);
+		saved_arm_div = readl_relaxed(ccm_base + CACRR);
+		writel_relaxed(arm_div_for_wait, ccm_base + CACRR);
 	} else {
-		clk_set_rate(clks[IMX6SL_CLK_ARM], saved_arm_rate);
+		writel_relaxed(saved_arm_div, ccm_base + CACRR);
 	}
+	while (__raw_readl(ccm_base + CDHIPR) & BM_CDHIPR_ARM_PODF_BUSY)
+		;
+
+	if (arm_div_for_wait == ARM_WAIT_DIV_396M)
+		imx6sl_enable_pll_arm(false);
 }
 
 static void __init imx6sl_clocks_init(struct device_node *ccm_node)
@@ -111,6 +180,7 @@ static void __init imx6sl_clocks_init(struct device_node *ccm_node)
 	np = of_find_compatible_node(NULL, NULL, "fsl,imx6sl-anatop");
 	base = of_iomap(np, 0);
 	WARN_ON(!base);
+	anatop_base = base;
 
 	/*                                             type               name            parent  base         div_mask */
 	clks[IMX6SL_CLK_PLL1_SYS]      = imx_clk_pllv3(IMX_PLLV3_SYS,	  "pll1_sys",	   "osc", base,        0x7f);
@@ -158,6 +228,7 @@ static void __init imx6sl_clocks_init(struct device_node *ccm_node)
 	np = ccm_node;
 	base = of_iomap(np, 0);
 	WARN_ON(!base);
+	ccm_base = base;
 
 	/* Reuse imx6q pm code */
 	imx6q_pm_set_ccm_base(base);