hwmon: Add xgene hwmon driver

This patch adds hardware temperature and power reading support for
APM X-Gene SoC using the mailbox communication interface.
Signed-off-by: NHoan Tran <hotran@apm.com>
Reviewed-by: NGuenter Roeck <linux@roeck-us.net>
Signed-off-by: NGuenter Roeck <linux@roeck-us.net>

Documentation/hwmon/xgene-hwmon

+Kernel driver xgene-hwmon
+========================
+
+Supported chips:
+ * APM X-Gene SoC
+
+Description
+-----------
+
+This driver adds hardware temperature and power reading support for
+APM X-Gene SoC using the mailbox communication interface.
+For device tree, it is the standard DT mailbox.
+For ACPI, it is the PCC mailbox.
+
+The following sensors are supported
+
+  * Temperature
+    - SoC on-die temperature in milli-degree C
+    - Alarm when high/over temperature occurs
+  * Power
+    - CPU power in uW
+    - IO power in uW
+
+sysfs-Interface
+---------------
+
+temp0_input - SoC on-die temperature (milli-degree C)
+temp0_critical_alarm - An 1 would indicates on-die temperature exceeded threshold
+power0_input - CPU power in (uW)
+power1_input - IO power in (uW)

drivers/hwmon/Kconfig

@@ -1823,6 +1823,13 @@ config SENSORS_ULTRA45
 	  This driver provides support for the Ultra45 workstation environmental
 	  sensors.
 
+config SENSORS_XGENE
+	tristate "APM X-Gene SoC hardware monitoring driver"
+	depends on XGENE_SLIMPRO_MBOX || PCC
+	help
+	  If you say yes here you get support for the temperature
+	  and power sensors for APM X-Gene SoC.
+
 if ACPI
 
 comment "ACPI drivers"

drivers/hwmon/Makefile

@@ -165,6 +165,7 @@ obj-$(CONFIG_SENSORS_W83L785TS)	+= w83l785ts.o
 obj-$(CONFIG_SENSORS_W83L786NG)	+= w83l786ng.o
 obj-$(CONFIG_SENSORS_WM831X)	+= wm831x-hwmon.o
 obj-$(CONFIG_SENSORS_WM8350)	+= wm8350-hwmon.o
+obj-$(CONFIG_SENSORS_XGENE)	+= xgene-hwmon.o
 
 obj-$(CONFIG_PMBUS)		+= pmbus/
 

drivers/hwmon/xgene-hwmon.c

+/*
+ * APM X-Gene SoC Hardware Monitoring Driver
+ *
+ * Copyright (c) 2016, Applied Micro Circuits Corporation
+ * Author: Loc Ho <lho@apm.com>
+ *         Hoan Tran <hotran@apm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ *
+ * This driver provides the following features:
+ *  - Retrieve CPU total power (uW)
+ *  - Retrieve IO total power (uW)
+ *  - Retrieve SoC temperature (milli-degree C) and alarm
+ */
+#include <linux/acpi.h>
+#include <linux/dma-mapping.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/interrupt.h>
+#include <linux/kfifo.h>
+#include <linux/mailbox_controller.h>
+#include <linux/mailbox_client.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <acpi/acpi_io.h>
+#include <acpi/pcc.h>
+
+/* SLIMpro message defines */
+#define MSG_TYPE_DBG			0
+#define MSG_TYPE_ERR			7
+#define MSG_TYPE_PWRMGMT		9
+
+#define MSG_TYPE(v)			(((v) & 0xF0000000) >> 28)
+#define MSG_TYPE_SET(v)			(((v) << 28) & 0xF0000000)
+#define MSG_SUBTYPE(v)			(((v) & 0x0F000000) >> 24)
+#define MSG_SUBTYPE_SET(v)		(((v) << 24) & 0x0F000000)
+
+#define DBG_SUBTYPE_SENSOR_READ		4
+#define SENSOR_RD_MSG			0x04FFE902
+#define SENSOR_RD_EN_ADDR(a)		((a) & 0x000FFFFF)
+#define PMD_PWR_REG			0x20
+#define PMD_PWR_MW_REG			0x26
+#define SOC_PWR_REG			0x21
+#define SOC_PWR_MW_REG			0x27
+#define SOC_TEMP_REG			0x10
+
+#define TEMP_NEGATIVE_BIT		8
+#define SENSOR_INVALID_DATA		BIT(15)
+
+#define PWRMGMT_SUBTYPE_TPC		1
+#define TPC_ALARM			2
+#define TPC_GET_ALARM			3
+#define TPC_CMD(v)			(((v) & 0x00FF0000) >> 16)
+#define TPC_CMD_SET(v)			(((v) << 16) & 0x00FF0000)
+#define TPC_EN_MSG(hndl, cmd, type) \
+	(MSG_TYPE_SET(MSG_TYPE_PWRMGMT) | \
+	MSG_SUBTYPE_SET(hndl) | TPC_CMD_SET(cmd) | type)
+
+/* PCC defines */
+#define PCC_SIGNATURE_MASK		0x50424300
+#define PCCC_GENERATE_DB_INT		BIT(15)
+#define PCCS_CMD_COMPLETE		BIT(0)
+#define PCCS_SCI_DOORBEL		BIT(1)
+#define PCCS_PLATFORM_NOTIFICATION	BIT(3)
+/*
+ * Arbitrary retries in case the remote processor is slow to respond
+ * to PCC commands
+ */
+#define PCC_NUM_RETRIES			500
+
+#define ASYNC_MSG_FIFO_SIZE		16
+#define MBOX_OP_TIMEOUTMS		1000
+
+#define WATT_TO_mWATT(x)		((x) * 1000)
+#define mWATT_TO_uWATT(x)		((x) * 1000)
+#define CELSIUS_TO_mCELSIUS(x)		((x) * 1000)
+
+#define to_xgene_hwmon_dev(cl)		\
+	container_of(cl, struct xgene_hwmon_dev, mbox_client)
+
+struct slimpro_resp_msg {
+	u32 msg;
+	u32 param1;
+	u32 param2;
+} __packed;
+
+struct xgene_hwmon_dev {
+	struct device		*dev;
+	struct mbox_chan	*mbox_chan;
+	struct mbox_client	mbox_client;
+	int			mbox_idx;
+
+	spinlock_t		kfifo_lock;
+	struct mutex		rd_mutex;
+	struct completion	rd_complete;
+	int			resp_pending;
+	struct slimpro_resp_msg sync_msg;
+
+	struct work_struct	workq;
+	struct kfifo_rec_ptr_1	async_msg_fifo;
+
+	struct device		*hwmon_dev;
+	bool			temp_critical_alarm;
+
+	phys_addr_t		comm_base_addr;
+	void			*pcc_comm_addr;
+	u64			usecs_lat;
+};
+
+/*
+ * This function tests and clears a bitmask then returns its old value
+ */
+static u16 xgene_word_tst_and_clr(u16 *addr, u16 mask)
+{
+	u16 ret, val;
+
+	val = readw_relaxed(addr);
+	ret = val & mask;
+	val &= ~mask;
+	writew_relaxed(val, addr);
+
+	return ret;
+}
+
+static int xgene_hwmon_pcc_rd(struct xgene_hwmon_dev *ctx, u32 *msg)
+{
+	struct acpi_pcct_shared_memory *generic_comm_base = ctx->pcc_comm_addr;
+	void *ptr = generic_comm_base + 1;
+	int rc, i;
+	u16 val;
+
+	mutex_lock(&ctx->rd_mutex);
+	init_completion(&ctx->rd_complete);
+	ctx->resp_pending = true;
+
+	/* Write signature for subspace */
+	writel_relaxed(PCC_SIGNATURE_MASK | ctx->mbox_idx,
+		       &generic_comm_base->signature);
+
+	/* Write to the shared command region */
+	writew_relaxed(MSG_TYPE(msg[0]) | PCCC_GENERATE_DB_INT,
+		       &generic_comm_base->command);
+
+	/* Flip CMD COMPLETE bit */
+	val = readw_relaxed(&generic_comm_base->status);
+	val &= ~PCCS_CMD_COMPLETE;
+	writew_relaxed(val, &generic_comm_base->status);
+
+	/* Copy the message to the PCC comm space */
+	for (i = 0; i < sizeof(struct slimpro_resp_msg) / 4; i++)
+		writel_relaxed(msg[i], ptr + i * 4);
+
+	/* Ring the doorbell */
+	rc = mbox_send_message(ctx->mbox_chan, msg);
+	if (rc < 0) {
+		dev_err(ctx->dev, "Mailbox send error %d\n", rc);
+		goto err;
+	}
+	if (!wait_for_completion_timeout(&ctx->rd_complete,
+					 usecs_to_jiffies(ctx->usecs_lat))) {
+		dev_err(ctx->dev, "Mailbox operation timed out\n");
+		rc = -ETIMEDOUT;
+		goto err;
+	}
+
+	/* Check for error message */
+	if (MSG_TYPE(ctx->sync_msg.msg) == MSG_TYPE_ERR) {
+		rc = -EINVAL;
+		goto err;
+	}
+
+	msg[0] = ctx->sync_msg.msg;
+	msg[1] = ctx->sync_msg.param1;
+	msg[2] = ctx->sync_msg.param2;
+
+err:
+	mbox_chan_txdone(ctx->mbox_chan, 0);
+	ctx->resp_pending = false;
+	mutex_unlock(&ctx->rd_mutex);
+	return rc;
+}
+
+static int xgene_hwmon_rd(struct xgene_hwmon_dev *ctx, u32 *msg)
+{
+	int rc;
+
+	mutex_lock(&ctx->rd_mutex);
+	init_completion(&ctx->rd_complete);
+	ctx->resp_pending = true;
+
+	rc = mbox_send_message(ctx->mbox_chan, msg);
+	if (rc < 0) {
+		dev_err(ctx->dev, "Mailbox send error %d\n", rc);
+		goto err;
+	}
+
+	if (!wait_for_completion_timeout(&ctx->rd_complete,
+					 msecs_to_jiffies(MBOX_OP_TIMEOUTMS))) {
+		dev_err(ctx->dev, "Mailbox operation timed out\n");
+		rc = -ETIMEDOUT;
+		goto err;
+	}
+
+	/* Check for error message */
+	if (MSG_TYPE(ctx->sync_msg.msg) == MSG_TYPE_ERR) {
+		rc = -EINVAL;
+		goto err;
+	}
+
+	msg[0] = ctx->sync_msg.msg;
+	msg[1] = ctx->sync_msg.param1;
+	msg[2] = ctx->sync_msg.param2;
+
+err:
+	ctx->resp_pending = false;
+	mutex_unlock(&ctx->rd_mutex);
+	return rc;
+}
+
+static int xgene_hwmon_reg_map_rd(struct xgene_hwmon_dev *ctx, u32 addr,
+				  u32 *data)
+{
+	u32 msg[3];
+	int rc;
+
+	msg[0] = SENSOR_RD_MSG;
+	msg[1] = SENSOR_RD_EN_ADDR(addr);
+	msg[2] = 0;
+
+	if (acpi_disabled)
+		rc = xgene_hwmon_rd(ctx, msg);
+	else
+		rc = xgene_hwmon_pcc_rd(ctx, msg);
+
+	if (rc < 0)
+		return rc;
+
+	/*
+	 * Check if sensor data is valid.
+	 */
+	if (msg[1] & SENSOR_INVALID_DATA)
+		return -ENODATA;
+
+	*data = msg[1];
+
+	return rc;
+}
+
+static int xgene_hwmon_get_notification_msg(struct xgene_hwmon_dev *ctx,
+					    u32 *amsg)
+{
+	u32 msg[3];
+	int rc;
+
+	msg[0] = TPC_EN_MSG(PWRMGMT_SUBTYPE_TPC, TPC_GET_ALARM, 0);
+	msg[1] = 0;
+	msg[2] = 0;
+
+	rc = xgene_hwmon_pcc_rd(ctx, msg);
+	if (rc < 0)
+		return rc;
+
+	amsg[0] = msg[0];
+	amsg[1] = msg[1];
+	amsg[2] = msg[2];
+
+	return rc;
+}
+
+static int xgene_hwmon_get_cpu_pwr(struct xgene_hwmon_dev *ctx, u32 *val)
+{
+	u32 watt, mwatt;
+	int rc;
+
+	rc = xgene_hwmon_reg_map_rd(ctx, PMD_PWR_REG, &watt);
+	if (rc < 0)
+		return rc;
+
+	rc = xgene_hwmon_reg_map_rd(ctx, PMD_PWR_MW_REG, &mwatt);
+	if (rc < 0)
+		return rc;
+
+	*val = WATT_TO_mWATT(watt) + mwatt;
+	return 0;
+}
+
+static int xgene_hwmon_get_io_pwr(struct xgene_hwmon_dev *ctx, u32 *val)
+{
+	u32 watt, mwatt;
+	int rc;
+
+	rc = xgene_hwmon_reg_map_rd(ctx, SOC_PWR_REG, &watt);
+	if (rc < 0)
+		return rc;
+
+	rc = xgene_hwmon_reg_map_rd(ctx, SOC_PWR_MW_REG, &mwatt);
+	if (rc < 0)
+		return rc;
+
+	*val = WATT_TO_mWATT(watt) + mwatt;
+	return 0;
+}
+
+static int xgene_hwmon_get_temp(struct xgene_hwmon_dev *ctx, u32 *val)
+{
+	return xgene_hwmon_reg_map_rd(ctx, SOC_TEMP_REG, val);
+}
+
+/*
+ * Sensor temperature/power functions
+ */
+static ssize_t temp1_input_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	struct xgene_hwmon_dev *ctx = dev_get_drvdata(dev);
+	int rc, temp;
+	u32 val;
+
+	rc = xgene_hwmon_get_temp(ctx, &val);
+	if (rc < 0)
+		return rc;
+
+	temp = sign_extend32(val, TEMP_NEGATIVE_BIT);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", CELSIUS_TO_mCELSIUS(temp));
+}
+
+static ssize_t temp1_label_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "SoC Temperature\n");
+}
+
+static ssize_t temp1_critical_alarm_show(struct device *dev,
+					 struct device_attribute *devattr,
+					 char *buf)
+{
+	struct xgene_hwmon_dev *ctx = dev_get_drvdata(dev);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", ctx->temp_critical_alarm);
+}
+
+static ssize_t power1_label_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "CPU power\n");
+}
+
+static ssize_t power2_label_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "IO power\n");
+}
+
+static ssize_t power1_input_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct xgene_hwmon_dev *ctx = dev_get_drvdata(dev);
+	u32 val;
+	int rc;
+
+	rc = xgene_hwmon_get_cpu_pwr(ctx, &val);
+	if (rc < 0)
+		return rc;
+
+	return snprintf(buf, PAGE_SIZE, "%u\n", mWATT_TO_uWATT(val));
+}
+
+static ssize_t power2_input_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct xgene_hwmon_dev *ctx = dev_get_drvdata(dev);
+	u32 val;
+	int rc;
+
+	rc = xgene_hwmon_get_io_pwr(ctx, &val);
+	if (rc < 0)
+		return rc;
+
+	return snprintf(buf, PAGE_SIZE, "%u\n", mWATT_TO_uWATT(val));
+}
+
+static DEVICE_ATTR_RO(temp1_label);
+static DEVICE_ATTR_RO(temp1_input);
+static DEVICE_ATTR_RO(temp1_critical_alarm);
+static DEVICE_ATTR_RO(power1_label);
+static DEVICE_ATTR_RO(power1_input);
+static DEVICE_ATTR_RO(power2_label);
+static DEVICE_ATTR_RO(power2_input);
+
+static struct attribute *xgene_hwmon_attrs[] = {
+	&dev_attr_temp1_label.attr,
+	&dev_attr_temp1_input.attr,
+	&dev_attr_temp1_critical_alarm.attr,
+	&dev_attr_power1_label.attr,
+	&dev_attr_power1_input.attr,
+	&dev_attr_power2_label.attr,
+	&dev_attr_power2_input.attr,
+	NULL,
+};
+
+ATTRIBUTE_GROUPS(xgene_hwmon);
+
+static int xgene_hwmon_tpc_alarm(struct xgene_hwmon_dev *ctx,
+				 struct slimpro_resp_msg *amsg)
+{
+	ctx->temp_critical_alarm = !!amsg->param2;
+	sysfs_notify(&ctx->dev->kobj, NULL, "temp1_critical_alarm");
+
+	return 0;
+}
+
+static void xgene_hwmon_process_pwrmsg(struct xgene_hwmon_dev *ctx,
+				       struct slimpro_resp_msg *amsg)
+{
+	if ((MSG_SUBTYPE(amsg->msg) == PWRMGMT_SUBTYPE_TPC) &&
+	    (TPC_CMD(amsg->msg) == TPC_ALARM))
+		xgene_hwmon_tpc_alarm(ctx, amsg);
+}
+
+/*
+ * This function is called to process async work queue
+ */
+static void xgene_hwmon_evt_work(struct work_struct *work)
+{
+	struct slimpro_resp_msg amsg;
+	struct xgene_hwmon_dev *ctx;
+	int ret;
+
+	ctx = container_of(work, struct xgene_hwmon_dev, workq);
+	while (kfifo_out_spinlocked(&ctx->async_msg_fifo, &amsg,
+				    sizeof(struct slimpro_resp_msg),
+				    &ctx->kfifo_lock)) {
+		/*
+		 * If PCC, send a consumer command to Platform to get info
+		 * If Slimpro Mailbox, get message from specific FIFO
+		 */
+		if (!acpi_disabled) {
+			ret = xgene_hwmon_get_notification_msg(ctx,
+							       (u32 *)&amsg);
+			if (ret < 0)
+				continue;
+		}
+
+		if (MSG_TYPE(amsg.msg) == MSG_TYPE_PWRMGMT)
+			xgene_hwmon_process_pwrmsg(ctx, &amsg);
+	}
+}
+
+/*
+ * This function is called when the SLIMpro Mailbox received a message
+ */
+static void xgene_hwmon_rx_cb(struct mbox_client *cl, void *msg)
+{
+	struct xgene_hwmon_dev *ctx = to_xgene_hwmon_dev(cl);
+	struct slimpro_resp_msg amsg;
+
+	/*
+	 * Response message format:
+	 * msg[0] is the return code of the operation
+	 * msg[1] is the first parameter word
+	 * msg[2] is the second parameter word
+	 *
+	 * As message only supports dword size, just assign it.
+	 */
+
+	/* Check for sync query */
+	if (ctx->resp_pending &&
+	    ((MSG_TYPE(((u32 *)msg)[0]) == MSG_TYPE_ERR) ||
+	     (MSG_TYPE(((u32 *)msg)[0]) == MSG_TYPE_DBG &&
+	      MSG_SUBTYPE(((u32 *)msg)[0]) == DBG_SUBTYPE_SENSOR_READ) ||
+	     (MSG_TYPE(((u32 *)msg)[0]) == MSG_TYPE_PWRMGMT &&
+	      MSG_SUBTYPE(((u32 *)msg)[0]) == PWRMGMT_SUBTYPE_TPC &&
+	      TPC_CMD(((u32 *)msg)[0]) == TPC_ALARM))) {
+		ctx->sync_msg.msg = ((u32 *)msg)[0];
+		ctx->sync_msg.param1 = ((u32 *)msg)[1];
+		ctx->sync_msg.param2 = ((u32 *)msg)[2];
+
+		/* Operation waiting for response */
+		complete(&ctx->rd_complete);
+
+		return;
+	}
+
+	amsg.msg   = ((u32 *)msg)[0];
+	amsg.param1 = ((u32 *)msg)[1];
+	amsg.param2 = ((u32 *)msg)[2];
+
+	/* Enqueue to the FIFO */
+	kfifo_in_spinlocked(&ctx->async_msg_fifo, &amsg,
+			    sizeof(struct slimpro_resp_msg), &ctx->kfifo_lock);
+	/* Schedule the bottom handler */
+	schedule_work(&ctx->workq);
+}
+
+/*
+ * This function is called when the PCC Mailbox received a message
+ */
+static void xgene_hwmon_pcc_rx_cb(struct mbox_client *cl, void *msg)
+{
+	struct xgene_hwmon_dev *ctx = to_xgene_hwmon_dev(cl);
+	struct acpi_pcct_shared_memory *generic_comm_base = ctx->pcc_comm_addr;
+	struct slimpro_resp_msg amsg;
+
+	msg = generic_comm_base + 1;
+	/* Check if platform sends interrupt */
+	if (!xgene_word_tst_and_clr(&generic_comm_base->status,
+				    PCCS_SCI_DOORBEL))
+		return;
+
+	/*
+	 * Response message format:
+	 * msg[0] is the return code of the operation
+	 * msg[1] is the first parameter word
+	 * msg[2] is the second parameter word
+	 *
+	 * As message only supports dword size, just assign it.
+	 */
+
+	/* Check for sync query */
+	if (ctx->resp_pending &&
+	    ((MSG_TYPE(((u32 *)msg)[0]) == MSG_TYPE_ERR) ||
+	     (MSG_TYPE(((u32 *)msg)[0]) == MSG_TYPE_DBG &&
+	      MSG_SUBTYPE(((u32 *)msg)[0]) == DBG_SUBTYPE_SENSOR_READ) ||
+	     (MSG_TYPE(((u32 *)msg)[0]) == MSG_TYPE_PWRMGMT &&
+	      MSG_SUBTYPE(((u32 *)msg)[0]) == PWRMGMT_SUBTYPE_TPC &&
+	      TPC_CMD(((u32 *)msg)[0]) == TPC_ALARM))) {
+		/* Check if platform completes command */
+		if (xgene_word_tst_and_clr(&generic_comm_base->status,
+					   PCCS_CMD_COMPLETE)) {
+			ctx->sync_msg.msg = ((u32 *)msg)[0];
+			ctx->sync_msg.param1 = ((u32 *)msg)[1];
+			ctx->sync_msg.param2 = ((u32 *)msg)[2];
+
+			/* Operation waiting for response */
+			complete(&ctx->rd_complete);
+
+			return;
+		}
+	}
+
+	/*
+	 * Platform notifies interrupt to OSPM.
+	 * OPSM schedules a consumer command to get this information
+	 * in a workqueue. Platform must wait until OSPM has issued
+	 * a consumer command that serves this notification.
+	 */
+
+	/* Enqueue to the FIFO */
+	kfifo_in_spinlocked(&ctx->async_msg_fifo, &amsg,
+			    sizeof(struct slimpro_resp_msg), &ctx->kfifo_lock);
+	/* Schedule the bottom handler */
+	schedule_work(&ctx->workq);
+}
+
+static void xgene_hwmon_tx_done(struct mbox_client *cl, void *msg, int ret)
+{
+	if (ret) {
+		dev_dbg(cl->dev, "TX did not complete: CMD sent:%x, ret:%d\n",
+			*(u16 *)msg, ret);
+	} else {
+		dev_dbg(cl->dev, "TX completed. CMD sent:%x, ret:%d\n",
+			*(u16 *)msg, ret);
+	}
+}
+
+static int xgene_hwmon_probe(struct platform_device *pdev)
+{
+	struct xgene_hwmon_dev *ctx;
+	struct mbox_client *cl;
+	int rc;
+
+	ctx = devm_kzalloc(&pdev->dev, sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->dev = &pdev->dev;
+	platform_set_drvdata(pdev, ctx);
+	cl = &ctx->mbox_client;
+
+	/* Request mailbox channel */
+	cl->dev = &pdev->dev;
+	cl->tx_done = xgene_hwmon_tx_done;
+	cl->tx_block = false;
+	cl->tx_tout = MBOX_OP_TIMEOUTMS;
+	cl->knows_txdone = false;
+	if (acpi_disabled) {
+		cl->rx_callback = xgene_hwmon_rx_cb;
+		ctx->mbox_chan = mbox_request_channel(cl, 0);
+		if (IS_ERR(ctx->mbox_chan)) {
+			dev_err(&pdev->dev,
+				"SLIMpro mailbox channel request failed\n");
+			return -ENODEV;
+		}
+	} else {
+		struct acpi_pcct_hw_reduced *cppc_ss;
+
+		if (device_property_read_u32(&pdev->dev, "pcc-channel",
+					     &ctx->mbox_idx)) {
+			dev_err(&pdev->dev, "no pcc-channel property\n");
+			return -ENODEV;
+		}
+
+		cl->rx_callback = xgene_hwmon_pcc_rx_cb;
+		ctx->mbox_chan = pcc_mbox_request_channel(cl, ctx->mbox_idx);
+		if (IS_ERR(ctx->mbox_chan)) {
+			dev_err(&pdev->dev,
+				"PPC channel request failed\n");
+			return -ENODEV;
+		}
+
+		/*
+		 * The PCC mailbox controller driver should
+		 * have parsed the PCCT (global table of all
+		 * PCC channels) and stored pointers to the
+		 * subspace communication region in con_priv.
+		 */
+		cppc_ss = ctx->mbox_chan->con_priv;
+		if (!cppc_ss) {
+			dev_err(&pdev->dev, "PPC subspace not found\n");
+			rc = -ENODEV;
+			goto out_mbox_free;
+		}
+
+		if (!ctx->mbox_chan->mbox->txdone_irq) {
+			dev_err(&pdev->dev, "PCC IRQ not supported\n");
+			rc = -ENODEV;
+			goto out_mbox_free;
+		}
+
+		/*
+		 * This is the shared communication region
+		 * for the OS and Platform to communicate over.
+		 */
+		ctx->comm_base_addr = cppc_ss->base_address;
+		if (ctx->comm_base_addr) {
+			ctx->pcc_comm_addr =
+					acpi_os_ioremap(ctx->comm_base_addr,
+							cppc_ss->length);
+		} else {
+			dev_err(&pdev->dev, "Failed to get PCC comm region\n");
+			rc = -ENODEV;
+			goto out_mbox_free;
+		}
+
+		if (!ctx->pcc_comm_addr) {
+			dev_err(&pdev->dev,
+				"Failed to ioremap PCC comm region\n");
+			rc = -ENOMEM;
+			goto out_mbox_free;
+		}
+
+		/*
+		 * cppc_ss->latency is just a Nominal value. In reality
+		 * the remote processor could be much slower to reply.
+		 * So add an arbitrary amount of wait on top of Nominal.
+		 */
+		ctx->usecs_lat = PCC_NUM_RETRIES * cppc_ss->latency;
+	}
+
+	spin_lock_init(&ctx->kfifo_lock);
+	mutex_init(&ctx->rd_mutex);
+
+	rc = kfifo_alloc(&ctx->async_msg_fifo,
+			 sizeof(struct slimpro_resp_msg) * ASYNC_MSG_FIFO_SIZE,
+			 GFP_KERNEL);
+	if (rc)
+		goto out_mbox_free;
+
+	INIT_WORK(&ctx->workq, xgene_hwmon_evt_work);
+
+	ctx->hwmon_dev = hwmon_device_register_with_groups(ctx->dev,
+							   "apm_xgene",
+							   ctx,
+							   xgene_hwmon_groups);
+	if (IS_ERR(ctx->hwmon_dev)) {
+		dev_err(&pdev->dev, "Failed to register HW monitor device\n");
+		rc = PTR_ERR(ctx->hwmon_dev);
+		goto out;
+	}
+
+	dev_info(&pdev->dev, "APM X-Gene SoC HW monitor driver registered\n");
+
+	return 0;
+
+out:
+	kfifo_free(&ctx->async_msg_fifo);
+out_mbox_free:
+	if (acpi_disabled)
+		mbox_free_channel(ctx->mbox_chan);
+	else
+		pcc_mbox_free_channel(ctx->mbox_chan);
+
+	return rc;
+}
+
+static int xgene_hwmon_remove(struct platform_device *pdev)
+{
+	struct xgene_hwmon_dev *ctx = platform_get_drvdata(pdev);
+
+	hwmon_device_unregister(ctx->hwmon_dev);
+	kfifo_free(&ctx->async_msg_fifo);
+	if (acpi_disabled)
+		mbox_free_channel(ctx->mbox_chan);
+	else
+		pcc_mbox_free_channel(ctx->mbox_chan);
+
+	return 0;
+}
+
+#ifdef CONFIG_ACPI
+static const struct acpi_device_id xgene_hwmon_acpi_match[] = {
+	{"APMC0D29", 0},
+	{},
+};
+MODULE_DEVICE_TABLE(acpi, xgene_hwmon_acpi_match);
+#endif
+
+static const struct of_device_id xgene_hwmon_of_match[] = {
+	{.compatible = "apm,xgene-slimpro-hwmon"},
+	{}
+};
+MODULE_DEVICE_TABLE(of, xgene_hwmon_of_match);
+
+static struct platform_driver xgene_hwmon_driver __refdata = {
+	.probe = xgene_hwmon_probe,
+	.remove = xgene_hwmon_remove,
+	.driver = {
+		.name = "xgene-slimpro-hwmon",
+		.of_match_table = xgene_hwmon_of_match,
+		.acpi_match_table = ACPI_PTR(xgene_hwmon_acpi_match),
+	},
+};
+module_platform_driver(xgene_hwmon_driver);
+
+MODULE_DESCRIPTION("APM X-Gene SoC hardware monitor");
+MODULE_LICENSE("GPL");