[RFC PATCH v3] ARM: imx: Add basic imx6q thermal management

[RFC PATCH v3] ARM: imx: Add basic imx6q thermal management

[Robert Lee]

Based on v3.2 plus recently submitted cpu_cooling functionality here:

http://www.spinics.net/lists/linux-pm/msg26500.html

link to v2 submission:

http://www.spinics.net/lists/arm-kernel/msg155790.html

Changes since v2:
1. Fixed the various issues pointed out in v2
2. Made other code cleanup and a bit of re-organizing
3. Removed unecessary platform driver and device.

Performed some basic testing to ensure proper cooling operating.  If
you want to test this, full testing requires imx6q cpufreq
implementation (not yet in v3.2) and requires an imx6q part that has
temperature sensor calibration fuses correctly burned.

Robert Lee (1):
  ARM: imx: Add basic imx6q thermal management

 arch/arm/boot/dts/imx6q.dtsi    |    1 +
 drivers/thermal/Kconfig         |    6 +
 drivers/thermal/Makefile        |    1 +
 drivers/thermal/imx6q_thermal.c |  520 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 528 insertions(+), 0 deletions(-)
 create mode 100644 drivers/thermal/imx6q_thermal.c

[RFC PATCH v3] ARM: imx: Add basic imx6q thermal management

[Robert Lee]

Adds support for temperature sensor readings, registers with common
thermal framework, and uses the new common cpu_cooling interface.

Signed-off-by: Robert Lee <rob.lee@linaro.org>
---
 arch/arm/boot/dts/imx6q.dtsi    |    1 +
 drivers/thermal/Kconfig         |    6 +
 drivers/thermal/Makefile        |    1 +
 drivers/thermal/imx6q_thermal.c |  520 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 528 insertions(+), 0 deletions(-)
 create mode 100644 drivers/thermal/imx6q_thermal.c

diff --git a/arch/arm/boot/dts/imx6q.dtsi b/arch/arm/boot/dts/imx6q.dtsi
index 7dda599..d62b88d 100644
--- a/arch/arm/boot/dts/imx6q.dtsi
+++ b/arch/arm/boot/dts/imx6q.dtsi
@@ -508,6 +508,7 @@
 			};
 
 			ocotp at 021bc000 {
+				compatible = "fsl,imx6q-ocotp";
 				reg = <0x021bc000 0x4000>;
 			};
 
diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
index 298c1cd..dd8cede 100644
--- a/drivers/thermal/Kconfig
+++ b/drivers/thermal/Kconfig
@@ -29,3 +29,9 @@ config CPU_THERMAL
 	  This will be useful for platforms using the generic thermal interface
 	  and not the ACPI interface.
 	  If you want this support, you should say Y or M here.
+
+config IMX6Q_THERMAL
+	bool "IMX6Q Thermal interface support"
+	depends on THERMAL && CPU_THERMAL
+	help
+	  Adds thermal management for IMX6Q.
diff --git a/drivers/thermal/Makefile b/drivers/thermal/Makefile
index 655cbc4..e2bcffe 100644
--- a/drivers/thermal/Makefile
+++ b/drivers/thermal/Makefile
@@ -4,3 +4,4 @@
 
 obj-$(CONFIG_THERMAL)		+= thermal_sys.o
 obj-$(CONFIG_CPU_THERMAL)	+= cpu_cooling.o
+obj-$(CONFIG_IMX6Q_THERMAL)	+= imx6q_thermal.o
diff --git a/drivers/thermal/imx6q_thermal.c b/drivers/thermal/imx6q_thermal.c
new file mode 100644
index 0000000..3dbf8ae
--- /dev/null
+++ b/drivers/thermal/imx6q_thermal.c
@@ -0,0 +1,520 @@
+/*
+ * Copyright 2012 Freescale Semiconductor, Inc.
+ * Copyright 2012 Linaro Ltd.
+ *
+ * The code contained herein is licensed under the GNU General Public
+ * License. You may obtain a copy of the GNU General Public License
+ * Version 2 or later at the following locations:
+ *
+ * http://www.opensource.org/licenses/gpl-license.html
+ * http://www.gnu.org/copyleft/gpl.html
+ */
+
+/* i.MX6Q Thermal Implementation */
+
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/dmi.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/delay.h>
+#include <linux/types.h>
+#include <linux/thermal.h>
+#include <linux/io.h>
+#include <linux/syscalls.h>
+#include <linux/cpufreq.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/smp.h>
+#include <linux/cpu_cooling.h>
+#include <linux/platform_device.h>
+
+/* register define of anatop */
+#define HW_ANADIG_ANA_MISC0			0x00000150
+#define HW_ANADIG_ANA_MISC0_SET			0x00000154
+#define HW_ANADIG_ANA_MISC0_CLR			0x00000158
+#define HW_ANADIG_ANA_MISC0_TOG			0x0000015c
+#define BM_ANADIG_ANA_MISC0_REFTOP_SELBIASOFF	0x00000008
+
+#define HW_ANADIG_TEMPSENSE0			0x00000180
+#define HW_ANADIG_TEMPSENSE0_SET		0x00000184
+#define HW_ANADIG_TEMPSENSE0_CLR		0x00000188
+#define HW_ANADIG_TEMPSENSE0_TOG		0x0000018c
+
+#define BP_ANADIG_TEMPSENSE0_TEMP_VALUE		8
+#define BM_ANADIG_TEMPSENSE0_TEMP_VALUE		0x000FFF00
+#define BM_ANADIG_TEMPSENSE0_FINISHED		0x00000004
+#define BM_ANADIG_TEMPSENSE0_MEASURE_TEMP	0x00000002
+#define BM_ANADIG_TEMPSENSE0_POWER_DOWN		0x00000001
+
+#define HW_ANADIG_TEMPSENSE1			0x00000190
+#define HW_ANADIG_TEMPSENSE1_SET		0x00000194
+#define HW_ANADIG_TEMPSENSE1_CLR		0x00000198
+#define BP_ANADIG_TEMPSENSE1_MEASURE_FREQ	0
+#define BM_ANADIG_TEMPSENSE1_MEASURE_FREQ	0x0000FFFF
+
+#define HW_OCOTP_ANA1				0x000004E0
+
+#define IMX6Q_THERMAL_POLLING_FREQUENCY_MS 10000
+#define IMX6Q_THERMAL_ACT_TRP_PTS 3
+/* assumption: always one critical trip point */
+#define IMX6Q_THERMAL_TOTAL_TRP_PTS (IMX6Q_THERMAL_ACT_TRP_PTS + 1)
+
+struct th_sys_trip_point {
+	u32 temp; /* in celcius */
+	enum thermal_trip_type type;
+};
+
+struct imx6q_thermal_data {
+	struct th_sys_trip_point trp_pts[IMX6Q_THERMAL_TOTAL_TRP_PTS];
+	struct freq_pctg_table freq_tab[IMX6Q_THERMAL_ACT_TRP_PTS];
+};
+
+struct imx6q_sensor_data {
+	int	c1, c2;
+	char	*name;
+	u32	pre_susp_state;
+};
+
+struct imx6q_thermal_zone {
+	struct thermal_zone_device *therm_dev;
+	struct thermal_cooling_device *cool_dev;
+	struct imx6q_sensor_data sensor_data;
+	struct imx6q_thermal_data *thermal_data;
+};
+
+/*
+ * This data defines the various trip points that will trigger action
+ * when crossed.
+ */
+static struct imx6q_thermal_data thermal_data = {
+	.trp_pts[0] = {
+		.temp	 = 85000,
+		.type	 = THERMAL_TRIP_STATE_ACTIVE,
+	},
+	.freq_tab[0] = {
+		.freq_clip_pctg[0] = 25,
+	},
+	.trp_pts[1] = {
+		.temp	 = 90000,
+		.type	 = THERMAL_TRIP_STATE_ACTIVE,
+	},
+	.freq_tab[1] = {
+		.freq_clip_pctg[0] = 65,
+	},
+	.trp_pts[2] = {
+		.temp	 = 95000,
+		.type	 = THERMAL_TRIP_STATE_ACTIVE,
+	},
+	.freq_tab[2] = {
+		.freq_clip_pctg[0] = 99,
+	},
+	.trp_pts[3] = {
+		.temp	 = 100000,
+		.type	 = THERMAL_TRIP_CRITICAL,
+	},
+};
+
+static int th_sys_get_temp(struct thermal_zone_device *thermal,
+				  unsigned long *temp);
+
+static struct imx6q_thermal_zone	*th_zone;
+static void __iomem			*anatop_base, *ocotp_base;
+
+static inline int imx6q_get_temp(int *temp, struct imx6q_sensor_data *sd)
+{
+	unsigned int n_meas;
+	unsigned int reg;
+
+	/*
+	 * For now we only using single measure.  Every time we measure
+	 * the temperature, we will power on/down the anadig module
+	 */
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
+		anatop_base + HW_ANADIG_TEMPSENSE0_CLR);
+
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_MEASURE_TEMP,
+		anatop_base + HW_ANADIG_TEMPSENSE0_SET);
+
+	/*
+	 * According to SoC designers, it may require up to ~17us to complete
+	 * a measurement.  But we have a 'finished' status bit, so we
+	 * check it just in case the designers are liars.
+	 */
+	do
+		msleep(1);
+	while (!(readl_relaxed(anatop_base + HW_ANADIG_TEMPSENSE0)
+		& BM_ANADIG_TEMPSENSE0_FINISHED));
+
+	reg = readl_relaxed(anatop_base + HW_ANADIG_TEMPSENSE0);
+
+	n_meas = (reg & BM_ANADIG_TEMPSENSE0_TEMP_VALUE)
+			>> BP_ANADIG_TEMPSENSE0_TEMP_VALUE;
+
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_MEASURE_TEMP,
+		anatop_base + HW_ANADIG_TEMPSENSE0_CLR);
+
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
+			anatop_base + HW_ANADIG_TEMPSENSE0_SET);
+
+	/* See imx6q_thermal_process_fuse_data for forumla derivation. */
+	*temp = sd->c2 + (sd->c1 * n_meas);
+
+	pr_debug("Temperature: %d\n", *temp / 1000);
+
+	return 0;
+}
+
+static int th_sys_get_temp(struct thermal_zone_device *thermal,
+				  unsigned long *temp)
+{
+	int tmp = 0;
+
+	struct imx6q_sensor_data *sd;
+
+	sd = &(((struct imx6q_thermal_zone *)thermal->devdata)->sensor_data);
+
+	imx6q_get_temp(&tmp, sd);
+
+	/*
+	 * The thermal framework code stores temperature in unsigned long. Also,
+	 * it has references to "millicelcius" which limits the lowest
+	 * temperature possible (compared to Kelvin).
+	 */
+	if (tmp > 0)
+		*temp = tmp;
+	else
+		*temp = 0;
+
+	return 0;
+}
+
+static int th_sys_get_mode(struct thermal_zone_device *thermal,
+			    enum thermal_device_mode *mode)
+{
+	*mode = THERMAL_DEVICE_ENABLED;
+	return 0;
+}
+
+static int th_sys_get_trip_type(struct thermal_zone_device *thermal, int trip,
+				 enum thermal_trip_type *type)
+{
+	struct imx6q_thermal_data *p;
+
+	if (trip >= IMX6Q_THERMAL_TOTAL_TRP_PTS)
+		return -EINVAL;
+
+	p = ((struct imx6q_thermal_zone *)thermal->devdata)->thermal_data;
+
+	*type = p->trp_pts[trip].type;
+
+	return 0;
+}
+
+static int th_sys_get_trip_temp(struct thermal_zone_device *thermal, int trip,
+				 unsigned long *temp)
+{
+	struct imx6q_thermal_data *p;
+
+	if (trip >= IMX6Q_THERMAL_TOTAL_TRP_PTS)
+		return -EINVAL;
+
+	p = ((struct imx6q_thermal_zone *)thermal->devdata)->thermal_data;
+
+	*temp = p->trp_pts[trip].temp;
+
+	return 0;
+}
+
+static int th_sys_get_crit_temp(struct thermal_zone_device *thermal,
+				 unsigned long *temp)
+{
+	struct imx6q_thermal_data *p;
+
+	p = ((struct imx6q_thermal_zone *)thermal->devdata)->thermal_data;
+
+	*temp = p->trp_pts[IMX6Q_THERMAL_TOTAL_TRP_PTS - 1].temp;
+
+	return 0;
+}
+
+static int th_sys_bind(struct thermal_zone_device *thermal,
+			struct thermal_cooling_device *cdev)
+{
+	int i;
+	struct thermal_cooling_device *cd;
+
+	cd = ((struct imx6q_thermal_zone *)thermal->devdata)->cool_dev;
+
+	/* if the cooling device is the one from imx6 bind it */
+	if (cdev != cd)
+		return 0;
+
+	for (i = 0; i < IMX6Q_THERMAL_ACT_TRP_PTS; i++) {
+		if (thermal_zone_bind_cooling_device(thermal, i, cdev)) {
+			pr_err("error binding cooling dev\n");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static int th_sys_unbind(struct thermal_zone_device *thermal,
+			  struct thermal_cooling_device *cdev)
+{
+	int i;
+
+	struct thermal_cooling_device *cd;
+
+	cd = ((struct imx6q_thermal_zone *)thermal->devdata)->cool_dev;
+
+	if (cdev != cd)
+		return 0;
+
+	for (i = 0; i < IMX6Q_THERMAL_ACT_TRP_PTS; i++) {
+		if (thermal_zone_unbind_cooling_device(thermal, i, cdev)) {
+			pr_err("error unbinding cooling dev\n");
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
+static struct thermal_zone_device_ops imx6q_dev_ops = {
+	.bind = th_sys_bind,
+	.unbind = th_sys_unbind,
+	.get_temp = th_sys_get_temp,
+	.get_mode = th_sys_get_mode,
+	.get_trip_type = th_sys_get_trip_type,
+	.get_trip_temp = th_sys_get_trip_temp,
+	.get_crit_temp = th_sys_get_crit_temp,
+};
+
+static int imx6q_thermal_process_fuse_data(unsigned int fuse_data,
+		 struct imx6q_sensor_data *sd)
+{
+	int t1, t2, n1, n2;
+
+	if (fuse_data == 0 || fuse_data == 0xffffffff)
+		return -EINVAL;
+
+	/*
+	 * Fuse data layout:
+	 * [31:20] sensor value @ 25C
+	 * [19:8] sensor value of hot
+	 * [7:0] hot temperature value
+	 */
+	n1 = fuse_data >> 20;
+	n2 = (fuse_data & 0xfff00) >> 8;
+	t2 = fuse_data & 0xff;
+	t1 = 25; /* t1 always 25C */
+
+	pr_debug(" -- temperature sensor calibration data --\n");
+	pr_debug("HW_OCOTP_ANA1: %x\n", fuse_data);
+	pr_debug("n1: %d\nn2: %d\nt1: %d\nt2: %d\n", n1, n2, t1, t2);
+
+	/*
+	 * Derived from linear interpolation,
+	 * Tmeas = T2 + (Nmeas - N2) * (T1 - T2) / (N1 - N2)
+	 * We want to reduce this down to the minimum computation necessary
+	 * for each temperature read.  Also, we want Tmeas in millicelcius
+	 * and we don't want to lose precision from integer division. So...
+	 * milli_Tmeas = 1000 * T2 + 1000 * (Nmeas - N2) * (T1 - T2) / (N1 - N2)
+	 * Let constant c1 = 1000 * (T1 - T2) / (N1 - N2)
+	 * milli_Tmeas = (1000 * T2) + c1 * (Nmeas - N2)
+	 * milli_Tmeas = (1000 * T2) + (c1 * Nmeas) - (c1 * N2)
+	 * Let constant c2 = (1000 * T2) - (c1 * N2)
+	 * milli_Tmeas = c2 + (c1 * Nmeas)
+	 */
+	sd->c1 = (1000 * (t1 - t2)) / (n1 - n2);
+	sd->c2 = (1000 * t2) - (sd->c1 * n2);
+
+	pr_debug("c1: %i\n", sd->c1);
+	pr_debug("c2: %i\n", sd->c2);
+
+	return 0;
+}
+
+static int imx6q_thermal_suspend(struct device *dev,
+						pm_message_t state)
+{
+	struct thermal_zone_device *tzd;
+	struct imx6q_sensor_data *sd;
+
+	tzd = container_of(dev, struct thermal_zone_device, device);
+
+	sd = &(((struct imx6q_thermal_zone *)tzd->devdata)->sensor_data);
+
+	sd->pre_susp_state = readl_relaxed(HW_ANADIG_TEMPSENSE0);
+
+	/* stop and power down temp sensor */
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_MEASURE_TEMP,
+		anatop_base + HW_ANADIG_TEMPSENSE0_CLR);
+
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
+		anatop_base + HW_ANADIG_TEMPSENSE0_SET);
+
+	return 0;
+}
+
+static int imx6q_thermal_resume(struct device *dev)
+{
+	struct thermal_zone_device *tzd;
+	struct imx6q_sensor_data *sd;
+
+	tzd = container_of(dev, struct thermal_zone_device, device);
+
+	sd = &(((struct imx6q_thermal_zone *)(tzd->devdata))->sensor_data);
+
+	if (!(sd->pre_susp_state & BM_ANADIG_TEMPSENSE0_POWER_DOWN))
+		writel_relaxed(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
+			anatop_base + HW_ANADIG_TEMPSENSE0_CLR);
+
+	if (sd->pre_susp_state & BM_ANADIG_TEMPSENSE0_MEASURE_TEMP)
+		writel_relaxed(BM_ANADIG_TEMPSENSE0_MEASURE_TEMP,
+			anatop_base + HW_ANADIG_TEMPSENSE0_CLR);
+
+	return 0;
+}
+
+static void __exit imx6q_thermal_exit(void)
+{
+	struct device_node *np_ocotp, *np_anatop;
+
+	if (th_zone && th_zone->therm_dev)
+		thermal_zone_device_unregister(th_zone->therm_dev);
+
+	if (th_zone && th_zone->cool_dev)
+		cpufreq_cooling_unregister();
+
+	kfree(th_zone);
+
+	if (ocotp_base)	{
+		np_ocotp = of_find_compatible_node(
+				NULL, NULL, "fsl,imx6q-ocotp");
+		if (np_ocotp)
+			iounmap(np_ocotp);
+	}
+
+	if (anatop_base) {
+		np_anatop = of_find_compatible_node(
+				NULL, NULL, "fsl,imx6q-anatop");
+		if (np_anatop)
+			iounmap(np_anatop);
+	}
+
+	pr_info("i.MX6Q: Kernel Thermal management unregistered\n");
+}
+
+static int __init imx6q_thermal_init(void)
+{
+	struct device_node *np_ocotp, *np_anatop;
+	unsigned int fuse_data;
+	int ret;
+
+	np_ocotp = of_find_compatible_node(NULL, NULL, "fsl,imx6q-ocotp");
+	np_anatop = of_find_compatible_node(NULL, NULL, "fsl,imx6q-anatop");
+
+	if (!(np_ocotp && np_anatop))
+		return -ENXIO; /* not a compatible platform */
+
+	ocotp_base = of_iomap(np_ocotp, 0);
+
+	if (!ocotp_base) {
+		pr_err("Could not retrieve ocotp-base\n");
+		ret = -ENXIO;
+		goto err_unregister;
+	}
+
+	anatop_base = of_iomap(np_anatop, 0);
+
+	if (!anatop_base) {
+		pr_err("Could not retrieve anantop-base\n");
+		ret = -ENXIO;
+		goto err_unregister;
+	}
+
+	fuse_data = readl_relaxed(ocotp_base + HW_OCOTP_ANA1);
+
+	th_zone = kzalloc(sizeof(struct imx6q_thermal_zone), GFP_KERNEL);
+
+	if (!th_zone) {
+		ret = -ENOMEM;
+		goto err_unregister;
+	}
+
+	th_zone->sensor_data.name = "imx6q-temp_sens";
+
+	ret = imx6q_thermal_process_fuse_data(fuse_data, &th_zone->sensor_data);
+
+	if (ret) {
+		pr_err("Invalid temperature calibration data.\n");
+		goto err_unregister;
+	}
+
+	/* Make sure sensor is in known good state for measurements */
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
+			anatop_base + HW_ANADIG_TEMPSENSE0_CLR);
+
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_MEASURE_TEMP,
+			anatop_base + HW_ANADIG_TEMPSENSE0_CLR);
+
+	writel_relaxed(BM_ANADIG_TEMPSENSE1_MEASURE_FREQ,
+			anatop_base + HW_ANADIG_TEMPSENSE1_CLR);
+
+	writel_relaxed(BM_ANADIG_ANA_MISC0_REFTOP_SELBIASOFF,
+			anatop_base + HW_ANADIG_ANA_MISC0_SET);
+
+	writel_relaxed(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
+			anatop_base + HW_ANADIG_TEMPSENSE0_SET);
+
+	th_zone->thermal_data = &thermal_data;
+
+	if (!th_zone->thermal_data) {
+		pr_err("Temperature sensor data not initialised\n");
+		ret = -EINVAL;
+		goto err_unregister;
+	}
+
+	th_zone->cool_dev = cpufreq_cooling_register(
+		(struct freq_pctg_table *)th_zone->thermal_data->freq_tab,
+		IMX6Q_THERMAL_ACT_TRP_PTS, cpumask_of(0));
+
+	if (IS_ERR(th_zone->cool_dev)) {
+		pr_err("Failed to register cpufreq cooling device\n");
+		ret = -EINVAL;
+		goto err_unregister;
+	}
+
+	th_zone->therm_dev = thermal_zone_device_register(
+		th_zone->sensor_data.name, IMX6Q_THERMAL_TOTAL_TRP_PTS,
+		th_zone, &imx6q_dev_ops, 0, 0, 0,
+		IMX6Q_THERMAL_POLLING_FREQUENCY_MS);
+
+	if (IS_ERR(th_zone->therm_dev)) {
+		pr_err("Failed to register thermal zone device\n");
+		ret = -EINVAL;
+		goto err_unregister;
+	}
+
+	/* In the rarest of cases, order matters here - resume goes first */
+	th_zone->therm_dev->device.class->resume = imx6q_thermal_resume;
+	th_zone->therm_dev->device.class->suspend = imx6q_thermal_suspend;
+
+	return 0;
+
+err_unregister:
+	imx6q_thermal_exit();
+	return ret;
+}
+
+module_init(imx6q_thermal_init);
+module_exit(imx6q_thermal_exit);
+
+MODULE_AUTHOR("Freescale Semiconductor");
+MODULE_DESCRIPTION("i.MX6Q SoC thermal driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:imx6q-thermal");
-- 
1.7.1

[RFC PATCH v3] ARM: imx: Add basic imx6q thermal management

[Rob Lee]

> + ? ? ? /* In the rarest of cases, order matters here - resume goes first */
> + ? ? ? th_zone->therm_dev->device.class->resume = imx6q_thermal_resume;
> + ? ? ? th_zone->therm_dev->device.class->suspend = imx6q_thermal_suspend;
On second thought, I should have barrier between these two statements
to guarantee order.  I think mb() would be ok.

[RFC PATCH v3] ARM: imx: Add basic imx6q thermal management

[Russell King - ARM Linux]

On Wed, Jan 18, 2012 at 05:40:02AM -0600, Rob Lee wrote:
> > + ? ? ? /* In the rarest of cases, order matters here - resume goes first */
> > + ? ? ? th_zone->therm_dev->device.class->resume = imx6q_thermal_resume;
> > + ? ? ? th_zone->therm_dev->device.class->suspend = imx6q_thermal_suspend;
> On second thought, I should have barrier between these two statements
> to guarantee order.  I think mb() would be ok.

Err, no.  This is a serious bug.

You're writing to this structure:

static struct class thermal_class = {
        .name = "thermal",
        .dev_release = thermal_release,
};

in thermal_sys.c, which would be shared with other thermal drivers.  This
is far from safe - it's insane.

The ordering or mb() is the least of your problems.

If there isn't suspend/resume support provided, please talk to the thermal
people about how to do this.