ARM: imx6: initialize CCM_CLPCR_LPM into RUN mode earlier

Commit 4631960d26da ("ARM: imx6: set initial power mode in pm function") moves imx6_set_lpm() from clock init function into imx6_pm_common_init(). This causes a hang when cpuidle support is enabled. The reason for that is ARM core clock is shut down unexpectedly by WAIT mode. It happens with the following call stack:

    cpuidle_register_governor()
        cpuidle_switch_governor()
            cpuidle_uninstall_idle_handler()
                synchronize_sched()
                    wait_rcu_gp()
                        wait_for_completion()

When wait_for_completion() is called as above, all cores are idle/WFI. Hence, the reset value of CCM_CLPCR_LPM - WAIT mode, will trigger a hardware shutdown of the ARM core clock.

To fix the regression, we need to ensure that CCM_CLPCR_LPM is initialized into RUN mode earlier than cpuidle governor registration, which is a postcore_initcall. This patch creates function imx6_pm_ccm_init() to map CCM block and initialize CCM_CLPCR_LPM into RUN mode, and have the function called from machine .init_irq hook, which should be early enough.

Reported-by Kevin Hilman <[email protected]>

Fixes 4631960d26da ("ARM: imx6: set initial power mode in pm function")

Signed-off-by Shawn Guo <[email protected]>

---
 arch/arm/mach-imx/common.h      |  1 +
 arch/arm/mach-imx/mach-imx6q.c  |  1 +
 arch/arm/mach-imx/mach-imx6sl.c |  1 +
 arch/arm/mach-imx/mach-imx6sx.c |  1 +
 arch/arm/mach-imx/pm-imx6.c     | 28 ++++++++++++++++++----------
 5 files changed, 22 insertions(+), 10 deletions(-)

arch/arm/mach-imx/common.h +1 -0

index d1e2873f807e..fbd86f1b7f3b 100644
@@ -123,6 +123,7 @@ static inline void v7_cpu_resume(void) {}
 static inline void imx6_suspend(void __iomem *ocram_vbase) {}
 #endif
 
+void imx6_pm_ccm_init(const char *ccm_compat);
 void imx6q_pm_init(void);
 void imx6dl_pm_init(void);
 void imx6sl_pm_init(void);

arch/arm/mach-imx/mach-imx6q.c +1 -0

index 3ab61549ce0f..9602cc12d2f1 100644
@@ -393,6 +393,7 @@ static void __init imx6q_init_irq(void)
        imx_init_l2cache();
        imx_src_init();
        irqchip_init();
+       imx6_pm_ccm_init("fsl,imx6q-ccm");
 }
 
 static const char * const imx6q_dt_compat[] __initconst = {

arch/arm/mach-imx/mach-imx6sl.c +1 -0

index 12a1b098fc6a..300326373166 100644
@@ -66,6 +66,7 @@ static void __init imx6sl_init_irq(void)
        imx_init_l2cache();
        imx_src_init();
        irqchip_init();
+       imx6_pm_ccm_init("fsl,imx6sl-ccm");
 }
 
 static const char * const imx6sl_dt_compat[] __initconst = {

arch/arm/mach-imx/mach-imx6sx.c +1 -0

index f17b7004c24b..6a0b0614de29 100644
@@ -86,6 +86,7 @@ static void __init imx6sx_init_irq(void)
        imx_init_l2cache();
        imx_src_init();
        irqchip_init();
+       imx6_pm_ccm_init("fsl,imx6sx-ccm");
 }
 
 static void __init imx6sx_init_late(void)

arch/arm/mach-imx/pm-imx6.c +18 -11

index 27bc80dab2d8..b01650d94f91 100644
@@ -89,7 +89,6 @@ struct imx6_pm_base {
 
 struct imx6_pm_socdata {
        u32 ddr_type;
-       const char *ccm_compat;
        const char *mmdc_compat;
        const char *src_compat;
        const char *iomuxc_compat;

@@ -139,7 +138,6 @@ static const u32 imx6sx_mmdc_io_offset[] __initconst = {
 };
 
 static const struct imx6_pm_socdata imx6q_pm_data __initconst = {
-       .ccm_compat = "fsl,imx6q-ccm",
        .mmdc_compat = "fsl,imx6q-mmdc",
        .src_compat = "fsl,imx6q-src",
        .iomuxc_compat = "fsl,imx6q-iomuxc",

@@ -149,7 +147,6 @@ static const struct imx6_pm_socdata imx6q_pm_data __initconst = {
 };
 
 static const struct imx6_pm_socdata imx6dl_pm_data __initconst = {
-       .ccm_compat = "fsl,imx6q-ccm",
        .mmdc_compat = "fsl,imx6q-mmdc",
        .src_compat = "fsl,imx6q-src",
        .iomuxc_compat = "fsl,imx6dl-iomuxc",

@@ -159,7 +156,6 @@ static const struct imx6_pm_socdata imx6dl_pm_data __initconst = {
 };
 
 static const struct imx6_pm_socdata imx6sl_pm_data __initconst = {
-       .ccm_compat = "fsl,imx6sl-ccm",
        .mmdc_compat = "fsl,imx6sl-mmdc",
        .src_compat = "fsl,imx6sl-src",
        .iomuxc_compat = "fsl,imx6sl-iomuxc",

@@ -169,7 +165,6 @@ static const struct imx6_pm_socdata imx6sl_pm_data __initconst = {
 };
 
 static const struct imx6_pm_socdata imx6sx_pm_data __initconst = {
-       .ccm_compat = "fsl,imx6sx-ccm",
        .mmdc_compat = "fsl,imx6sx-mmdc",
        .src_compat = "fsl,imx6sx-src",
        .iomuxc_compat = "fsl,imx6sx-iomuxc",

@@ -553,16 +548,11 @@ put_node:
 static void __init imx6_pm_common_init(const struct imx6_pm_socdata
                                        *socdata)
 {
-       struct device_node *np;
        struct regmap *gpr;
        int ret;
 
-       np = of_find_compatible_node(NULL, NULL, socdata->ccm_compat);
-       ccm_base = of_iomap(np, 0);
        WARN_ON(!ccm_base);
 
-       imx6_set_lpm(WAIT_CLOCKED);
-
        if (IS_ENABLED(CONFIG_SUSPEND)) {
                ret = imx6q_suspend_init(socdata);
                if (ret)

@@ -583,6 +573,24 @@ static void __init imx6_pm_common_init(const struct imx6_pm_socdata
                                   IMX6Q_GPR1_GINT);
 }
 
+void __init imx6_pm_ccm_init(const char *ccm_compat)
+{
+       struct device_node *np;
+       u32 val;
+
+       np = of_find_compatible_node(NULL, NULL, ccm_compat);
+       ccm_base = of_iomap(np, 0);
+       BUG_ON(!ccm_base);
+
+       /*
+        * Initialize CCM_CLPCR_LPM into RUN mode to avoid ARM core
+        * clock being shut down unexpectedly by WAIT mode.
+        */
+       val = readl_relaxed(ccm_base + CLPCR);
+       val &= ~BM_CLPCR_LPM;
+       writel_relaxed(val, ccm_base + CLPCR);
+}
+
 void __init imx6q_pm_init(void)
 {
        imx6_pm_common_init(&imx6q_pm_data);
--

1.9.1

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Quoted 24 lines · Shawn Guo

Commit 4631960d26da ("ARM: imx6: set initial power mode in pm function") moves imx6_set_lpm() from clock init function into imx6_pm_common_init(). This causes a hang when cpuidle support is enabled. The reason for that is ARM core clock is shut down unexpectedly by WAIT mode. It happens with the following call stack:

    cpuidle_register_governor()
        cpuidle_switch_governor()
            cpuidle_uninstall_idle_handler()
                synchronize_sched()
                    wait_rcu_gp()
                        wait_for_completion()

When wait_for_completion() is called as above, all cores are idle/WFI. Hence, the reset value of CCM_CLPCR_LPM - WAIT mode, will trigger a hardware shutdown of the ARM core clock.

To fix the regression, we need to ensure that CCM_CLPCR_LPM is initialized into RUN mode earlier than cpuidle governor registration, which is a postcore_initcall. This patch creates function imx6_pm_ccm_init() to map CCM block and initialize CCM_CLPCR_LPM into RUN mode, and have the function called from machine .init_irq hook, which should be early enough.

Quoted 3 lines

Reported-by Kevin Hilman <[email protected]>

Fixes 4631960d26da ("ARM: imx6: set initial power mode in pm function")

Signed-off-by Shawn Guo <[email protected]>

Tested-by Tyler Baker <[email protected]>

I have applied this patch on top of next-20150429[1] and build/boot tested it with the kernelci.org farm. With these results[2], I can confirm the IMX6 boot regression reported is fixed by this patch.