Date:   Wed,  7 Jun 2017 17:10:06 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Roy Franz <roy.franz@...ium.com>,
        Harb Abdulhamid <harba@...eaurora.org>,
        Nishanth Menon <nm@...com>, Arnd Bergmann <arnd@...db.de>
Subject: [RFC PATCH 2/8] firmware: arm_scmi: add basic driver infrastructure for SCMI

The SCMI is intended to allow OSPM to manage various functions that are
provided by the hardware platform it is running on, including power and
performance functions. SCMI provides two levels of abstraction, protocols
and transports. Protocols define individual groups of system control and
management messages. A protocol specification describes the messages
that it supports. Transports describe the method by which protocol
messages are communicated between agents and the platform.

This patch adds basic infrastructure to manage the message allocation,
initialisation, packing/unpacking and shared memory management.

Signed-off-by: Sudeep Holla <sudeep.holla@....com>
---
 drivers/firmware/Kconfig           |  21 ++
 drivers/firmware/Makefile          |   1 +
 drivers/firmware/arm_scmi/Makefile |   2 +
 drivers/firmware/arm_scmi/common.h |  74 ++++
 drivers/firmware/arm_scmi/driver.c | 737 +++++++++++++++++++++++++++++++++++++
 include/linux/scmi_protocol.h      |  48 +++
 6 files changed, 883 insertions(+)
 create mode 100644 drivers/firmware/arm_scmi/Makefile
 create mode 100644 drivers/firmware/arm_scmi/common.h
 create mode 100644 drivers/firmware/arm_scmi/driver.c
 create mode 100644 include/linux/scmi_protocol.h

diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index 6e4ed5a9c6fd..c3d1a12763ce 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -19,6 +19,27 @@ config ARM_PSCI_CHECKER
 	  on and off through hotplug, so for now torture tests and PSCI checker
 	  are mutually exclusive.
 
+config ARM_SCMI_PROTOCOL
+	tristate "ARM System Control and Management Interface (SCMI) Message Protocol"
+	depends on ARM || ARM64 || COMPILE_TEST
+	depends on MAILBOX
+	help
+	  ARM System Control and Management Interface (SCMI) protocol is a
+	  set of operating system-independent software interfaces that are
+	  used in system management. SCMI is extensible and currently provides
+	  interfaces for: Discovery and self-description of the interfaces
+	  it supports, Power domain management which is the ability to place
+	  a given device or domain into the various power-saving states that
+	  it supports, Performance management which is the ability to control
+	  the performance of a domain that is composed of compute engines
+	  such as application processors and other accelerators, Clock
+	  management which is the ability to set and inquire rates on platform
+	  managed clocks and Sensor management which is the ability to read
+	  sensor data, and be notified of sensor value.
+
+	  This protocol library provides interface for all the client drivers
+	  making use of the features offered by the SCMI.
+
 config ARM_SCPI_PROTOCOL
 	tristate "ARM System Control and Power Interface (SCPI) Message Protocol"
 	depends on ARM || ARM64 || COMPILE_TEST
diff --git a/drivers/firmware/Makefile b/drivers/firmware/Makefile
index a37f12e8d137..91d3ff62c653 100644
--- a/drivers/firmware/Makefile
+++ b/drivers/firmware/Makefile
@@ -23,6 +23,7 @@ obj-$(CONFIG_QCOM_SCM_32)	+= qcom_scm-32.o
 CFLAGS_qcom_scm-32.o :=$(call as-instr,.arch armv7-a\n.arch_extension sec,-DREQUIRES_SEC=1) -march=armv7-a
 obj-$(CONFIG_TI_SCI_PROTOCOL)	+= ti_sci.o
 
+obj-$(CONFIG_ARM_SCMI_PROTOCOL)	+= arm_scmi/
 obj-y				+= broadcom/
 obj-y				+= meson/
 obj-$(CONFIG_GOOGLE_FIRMWARE)	+= google/
diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
new file mode 100644
index 000000000000..58e94c95e523
--- /dev/null
+++ b/drivers/firmware/arm_scmi/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_ARM_SCMI_PROTOCOL)	= arm_scmi.o
+arm_scmi-y = driver.o
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
new file mode 100644
index 000000000000..a3038efa3a8d
--- /dev/null
+++ b/drivers/firmware/arm_scmi/common.h
@@ -0,0 +1,74 @@
+/*
+ * System Control and Management Interface (SCMI) Message Protocol
+ * driver common header file containing some definitions, structures
+ * and function prototypes used in all the different SCMI protocols.
+ *
+ * Copyright (C) 2017 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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/>.
+ */
+
+#include <linux/completion.h>
+#include <linux/scmi_protocol.h>
+#include <linux/types.h>
+
+/**
+ * struct scmi_msg_hdr - Message(Tx/Rx) header
+ *
+ * @id: The identifier of the command being sent
+ * @protocol_id: The identifier of the protocol used to send @id command
+ * @seq: The token to identify the message. when a message/command returns,
+ *       the platform returns the whole message header unmodified including
+ *	 the token.
+ */
+struct scmi_msg_hdr {
+	u8 id;
+	u8 protocol_id;
+	u16 seq;
+	u32 status;
+	bool poll_completion;
+};
+
+/**
+ * struct scmi_msg - Message(Tx/Rx) structure
+ *
+ * @len: Length of data in the Buffer
+ * @buf: Buffer pointer
+ */
+struct scmi_msg {
+	u8 *buf;
+	size_t len;
+};
+
+/**
+ * struct scmi_xfer - Structure representing a message flow
+ *
+ * @hdr: Transmit message header
+ * @tx: Transmit message
+ * @rx: Receive message, the buffer should be pre-allocated to store
+ *	message. If request-ACK protocol is used, we can reuse the same
+ *	buffer for the rx path as we use for the tx path.
+ * @done: completion event
+ */
+
+struct scmi_xfer {
+	struct scmi_msg_hdr hdr;
+	struct scmi_msg tx;
+	struct scmi_msg rx;
+	struct completion done;
+};
+
+void scmi_put_one_xfer(struct scmi_handle *h, struct scmi_xfer *xfer);
+int scmi_do_xfer(struct scmi_handle *h, struct scmi_xfer *xfer);
+int scmi_one_xfer_init(struct scmi_handle *h, u8 msg_id, u8 msg_prot_id,
+		       size_t tx_size, size_t rx_size, struct scmi_xfer **p);
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
new file mode 100644
index 000000000000..f01e0643ac7d
--- /dev/null
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -0,0 +1,737 @@
+/*
+ * System Control and Management Interface (SCMI) Message Protocol driver
+ *
+ * SCMI Message Protocol is used between the System Control Processor(SCP)
+ * and the Application Processors(AP). The Message Handling Unit(MHU)
+ * provides a mechanism for inter-processor communication between SCP's
+ * Cortex M3 and AP.
+ *
+ * SCP offers control and management of the core/cluster power states,
+ * various power domain DVFS including the core/cluster, certain system
+ * clocks configuration, thermal sensors and many others.
+ *
+ * Copyright (C) 2017 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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/>.
+ */
+
+#include <linux/bitmap.h>
+#include <linux/export.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/mailbox_client.h>
+#include <linux/module.h>
+#include <linux/of_address.h>
+#include <linux/of_device.h>
+#include <linux/semaphore.h>
+#include <linux/slab.h>
+
+#include "common.h"
+
+#define MSG_ID_SHIFT		0
+#define MSG_ID_MASK		0xff
+#define MSG_TYPE_SHIFT		8
+#define MSG_TYPE_MASK		0x3
+#define MSG_PROTOCOL_ID_SHIFT	10
+#define MSG_PROTOCOL_ID_MASK	0xff
+#define MSG_TOKEN_ID_SHIFT	18
+#define MSG_TOKEN_ID_MASK	0x3ff
+#define MSG_XTRACT_TOKEN(header)	\
+	(((header) >> MSG_TOKEN_ID_SHIFT) & MSG_TOKEN_ID_MASK)
+
+enum scmi_error_codes {
+	SCMI_SUCCESS = 0,	/* Success */
+	SCMI_ERR_SUPPORT = -1,	/* Not supported */
+	SCMI_ERR_PARAMS = -2,	/* Invalid Parameters */
+	SCMI_ERR_ACCESS = -3,	/* Invalid access/permission denied */
+	SCMI_ERR_ENTRY = -4,	/* Not found */
+	SCMI_ERR_RANGE = -5,	/* Value out of range */
+	SCMI_ERR_BUSY = -6,	/* Device busy */
+	SCMI_ERR_COMMS = -7,	/* Communication Error */
+	SCMI_ERR_GENERIC = -8,	/* Generic Error */
+	SCMI_ERR_HARDWARE = -9,	/* Hardware Error */
+	SCMI_ERR_PROTOCOL = -10,/* Protocol Error */
+	SCMI_ERR_MAX
+};
+
+/* List of all  SCMI devices active in system */
+static LIST_HEAD(scmi_list);
+/* Protection for the entire list */
+static DEFINE_MUTEX(scmi_list_mutex);
+
+/**
+ * struct scmi_xfers_info - Structure to manage transfer information
+ *
+ * @sem_xfer_count: Counting Semaphore for managing max simultaneous
+ *	Messages.
+ * @xfer_block: Preallocated Message array
+ * @xfer_alloc_table: Bitmap table for allocated messages.
+ *	Index of this bitmap table is also used for message
+ *	sequence identifier.
+ * @xfer_lock: Protection for message allocation
+ */
+struct scmi_xfers_info {
+	struct semaphore sem_xfer_count;
+	struct scmi_xfer *xfer_block;
+	unsigned long *xfer_alloc_table;
+	/* protect transfer allocation */
+	spinlock_t xfer_lock;
+};
+
+/**
+ * struct scmi_desc - Description of SoC integration
+ *
+ * @max_rx_timeout_ms: Timeout for communication with SoC (in Milliseconds)
+ * @max_msg: Maximum number of messages that can be pending
+ *	simultaneously in the system
+ * @max_msg_size: Maximum size of data per message that can be handled.
+ */
+struct scmi_desc {
+	int max_rx_timeout_ms;
+	int max_msg;
+	int max_msg_size;
+};
+
+/**
+ * struct scmi_info - Structure representing a  SCMI instance
+ *
+ * @dev: Device pointer
+ * @desc: SoC description for this instance
+ * @handle: Instance of SCMI handle to send to clients
+ * @cl: Mailbox Client
+ * @tx_chan: Transmit mailbox channel
+ * @rx_chan: Receive mailbox channel
+ * @tx_payload: Transmit mailbox channel payload area
+ * @rx_payload: Receive mailbox channel payload area
+ * @minfo: Message info
+ * @node: list head
+ * @users: Number of users of this instance
+ */
+struct scmi_info {
+	struct device *dev;
+	const struct scmi_desc *desc;
+	struct scmi_handle handle;
+	struct mbox_client cl;
+	struct mbox_chan *tx_chan;
+	struct mbox_chan *rx_chan;
+	void __iomem *tx_payload;
+	void __iomem *rx_payload;
+	struct scmi_xfers_info minfo;
+	struct list_head node;
+	int users;
+};
+
+#define client_to_scmi_info(c)	container_of(c, struct scmi_info, cl)
+#define handle_to_scmi_info(h)	container_of(h, struct scmi_info, handle)
+
+/*
+ * The SCP firmware only executes in little-endian mode, so any buffers
+ * shared through SCMI should have their contents converted to little-endian
+ */
+struct scmi_shared_mem {
+	__le32 reserved;
+	__le32 channel_status;
+#define SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR	BIT(1)
+#define SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE	BIT(0)
+	__le32 reserved1[2];
+	__le32 flags;
+#define SCMI_SHMEM_FLAG_INTR_ENABLED	BIT(0)
+	__le32 length;
+	__le32 msg_header;
+	u8 msg_payload[0];
+} __packed;
+
+static int scmi_linux_errmap[] = {
+	/* better than switch case as long as return value is continuous */
+	0,			/* SCMI_SUCCESS */
+	-EOPNOTSUPP,		/* SCMI_ERR_SUPPORT */
+	-EINVAL,		/* SCMI_ERR_PARAM */
+	-EACCES,		/* SCMI_ERR_ACCESS */
+	-ENOENT,		/* SCMI_ERR_ENTRY */
+	-ERANGE,		/* SCMI_ERR_RANGE */
+	-EBUSY,			/* SCMI_ERR_BUSY */
+	-ECOMM,			/* SCMI_ERR_COMMS */
+	-EIO,			/* SCMI_ERR_GENERIC */
+	-EREMOTEIO,		/* SCMI_ERR_HARDWARE */
+	-EPROTO,		/* SCMI_ERR_PROTOCOL */
+};
+
+static inline int scmi_to_linux_errno(int errno)
+{
+	if (errno < SCMI_SUCCESS && errno > SCMI_ERR_MAX)
+		return scmi_linux_errmap[-errno];
+	return -EIO;
+}
+
+/**
+ * scmi_dump_header_dbg() - Helper to dump a message header.
+ *
+ * @dev: Device pointer corresponding to the SCMI entity
+ * @hdr: pointer to header.
+ */
+static inline void scmi_dump_header_dbg(struct device *dev,
+					struct scmi_msg_hdr *hdr)
+{
+	dev_dbg(dev, "Command ID: %x Sequence ID: %x Protocol: %x\n",
+		hdr->id, hdr->seq, hdr->protocol_id);
+}
+
+/**
+ * scmi_rx_callback() - mailbox client callback for receive messages
+ *
+ * @cl: client pointer
+ * @m: mailbox message
+ *
+ * Processes one received message to appropriate transfer information and
+ * signals completion of the transfer.
+ *
+ * NOTE: This function will be invoked in IRQ context, hence should be
+ * as optimal as possible.
+ */
+static void scmi_rx_callback(struct mbox_client *cl, void *m)
+{
+	u16 xfer_id;
+	struct scmi_xfer *xfer;
+	struct scmi_info *info = client_to_scmi_info(cl);
+	struct scmi_xfers_info *minfo = &info->minfo;
+	struct device *dev = info->dev;
+	struct scmi_shared_mem *mem = info->tx_payload;
+
+	xfer_id = MSG_XTRACT_TOKEN(mem->msg_header);
+
+	/*
+	 * Are we even expecting this?
+	 */
+	if (!test_bit(xfer_id, minfo->xfer_alloc_table)) {
+		dev_err(dev, "message for %d is not expected!\n", xfer_id);
+		return;
+	}
+
+	xfer = &minfo->xfer_block[xfer_id];
+
+	scmi_dump_header_dbg(dev, &xfer->hdr);
+	/* Is the message of valid length? */
+	if (xfer->rx.len > info->desc->max_msg_size) {
+		dev_err(dev, "unable to handle %lu xfer(max %d)\n",
+			xfer->rx.len, info->desc->max_msg_size);
+		return;
+	}
+
+	xfer->hdr.status = le32_to_cpu(*(__le32 *)mem->msg_payload);
+	/* Skip the length of header and statues in payload area i.e 8 bytes*/
+	xfer->rx.len = min_t(size_t, xfer->rx.len, mem->length - 8);
+
+	/* Take a copy to the rx buffer.. */
+	memcpy_fromio(xfer->rx.buf, mem->msg_payload + 4, xfer->rx.len);
+	complete(&xfer->done);
+}
+
+/**
+ * pack_scmi_header() - packs and returns 32-bit header
+ *
+ * @hdr: pointer to header containing all the information on message id,
+ *	protocol id and sequence id.
+ */
+static inline u32 pack_scmi_header(struct scmi_msg_hdr *hdr)
+{
+	return ((hdr->id & MSG_ID_MASK) << MSG_ID_SHIFT) |
+	   ((hdr->seq & MSG_TOKEN_ID_MASK) << MSG_TOKEN_ID_SHIFT) |
+	   ((hdr->protocol_id & MSG_PROTOCOL_ID_MASK) << MSG_PROTOCOL_ID_SHIFT);
+}
+
+/**
+ * scmi_tx_prepare() - mailbox client callback to prepare for the transfer
+ *
+ * @cl: client pointer
+ * @m: mailbox message
+ *
+ * This function prepares the shared memory which contains the header and the
+ * payload.
+ */
+static void scmi_tx_prepare(struct mbox_client *cl, void *m)
+{
+	struct scmi_xfer *t = m;
+	struct scmi_info *info = client_to_scmi_info(cl);
+	struct scmi_shared_mem *mem = info->tx_payload;
+
+	mem->channel_status = 0x0; /* Mark channel busy + clear error */
+	mem->flags = t->hdr.poll_completion ? 0 : SCMI_SHMEM_FLAG_INTR_ENABLED;
+	mem->length = sizeof(mem->msg_header) + t->tx.len;
+	mem->msg_header = cpu_to_le32(pack_scmi_header(&t->hdr));
+	if (t->tx.buf)
+		memcpy_toio(mem->msg_payload, t->tx.buf, t->tx.len);
+}
+
+/**
+ * scmi_one_xfer_get() - Allocate one message
+ *
+ * @handle: SCMI entity handle
+ *
+ * Helper function which is used by various command functions that are
+ * exposed to clients of this driver for allocating a message traffic event.
+ *
+ * This function can sleep depending on pending requests already in the system
+ * for the SCMI entity. Further, this also holds a spinlock to maintain
+ * integrity of internal data structures.
+ *
+ * Return: 0 if all went fine, else corresponding error.
+ */
+static struct scmi_xfer *scmi_one_xfer_get(struct scmi_handle *handle)
+{
+	u16 xfer_id;
+	int ret, timeout;
+	struct scmi_xfer *xfer;
+	unsigned long flags, bit_pos;
+	struct scmi_info *info = handle_to_scmi_info(handle);
+	struct scmi_xfers_info *minfo = &info->minfo;
+
+	/*
+	 * Ensure we have only controlled number of pending messages.
+	 * Ideally, we might just have to wait a single message, be
+	 * conservative and wait 5 times that..
+	 */
+	timeout = msecs_to_jiffies(info->desc->max_rx_timeout_ms) * 5;
+	ret = down_timeout(&minfo->sem_xfer_count, timeout);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	/* Keep the locked section as small as possible */
+	spin_lock_irqsave(&minfo->xfer_lock, flags);
+	bit_pos = find_first_zero_bit(minfo->xfer_alloc_table,
+				      info->desc->max_msg);
+	set_bit(bit_pos, minfo->xfer_alloc_table);
+	spin_unlock_irqrestore(&minfo->xfer_lock, flags);
+
+	xfer_id = bit_pos;
+
+	xfer = &minfo->xfer_block[xfer_id];
+	xfer->hdr.seq = xfer_id;
+	reinit_completion(&xfer->done);
+
+	return xfer;
+}
+
+/**
+ * scmi_put_one_xfer() - Release a message
+ *
+ * @minfo: transfer info pointer
+ * @xfer: message that was reserved by scmi_one_xfer_get
+ *
+ * This holds a spinlock to maintain integrity of internal data structures.
+ */
+void scmi_put_one_xfer(struct scmi_handle *handle, struct scmi_xfer *xfer)
+{
+	u16 xfer_id;
+	unsigned long flags;
+	struct scmi_msg_hdr *hdr;
+	struct scmi_info *info = handle_to_scmi_info(handle);
+	struct scmi_xfers_info *minfo = &info->minfo;
+
+	hdr = (struct scmi_msg_hdr *)xfer->tx.buf;
+	xfer_id = hdr->seq;
+
+	/*
+	 * Keep the locked section as small as possible
+	 * NOTE: we might escape with smp_mb and no lock here..
+	 * but just be conservative and symmetric.
+	 */
+	spin_lock_irqsave(&minfo->xfer_lock, flags);
+	clear_bit(xfer_id, minfo->xfer_alloc_table);
+	spin_unlock_irqrestore(&minfo->xfer_lock, flags);
+
+	/* Increment the count for the next user to get through */
+	up(&minfo->sem_xfer_count);
+}
+
+/**
+ * scmi_do_xfer() - Do one transfer
+ *
+ * @info: Pointer to SCMI entity information
+ * @xfer: Transfer to initiate and wait for response
+ *
+ * Return: -ETIMEDOUT in case of no response, if transmit error,
+ *   return corresponding error, else if all goes well,
+ *   return 0.
+ */
+int scmi_do_xfer(struct scmi_handle *handle, struct scmi_xfer *xfer)
+{
+	int ret;
+	int timeout;
+	struct scmi_info *info = handle_to_scmi_info(handle);
+	struct device *dev = info->dev;
+
+	ret = mbox_send_message(info->tx_chan, xfer);
+	if (ret < 0) {
+		dev_dbg(dev, "mbox send fail %d\n", ret);
+		return ret;
+	}
+
+	/* mbox_send_message returns non-negative value on success, so reset */
+	ret = 0;
+
+	/* And we wait for the response. */
+	timeout = msecs_to_jiffies(info->desc->max_rx_timeout_ms);
+	if (!wait_for_completion_timeout(&xfer->done, timeout)) {
+		dev_err(dev, "mbox timed out in resp(caller: %pF)\n",
+			(void *)_RET_IP_);
+		ret = -ETIMEDOUT;
+	} else if (xfer->hdr.status) {
+		ret = scmi_to_linux_errno(xfer->hdr.status);
+	}
+	/*
+	 * NOTE: we might prefer not to need the mailbox ticker to manage the
+	 * transfer queueing since the protocol layer queues things by itself.
+	 * Unfortunately, we have to kick the mailbox framework after we have
+	 * received our message.
+	 */
+	mbox_client_txdone(info->tx_chan, ret);
+
+	return ret;
+}
+
+/**
+ * scmi_one_xfer_init() - Allocate and initialise one message
+ *
+ * @handle: SCMI entity handle
+ * @msg_id: Message identifier
+ * @msg_prot_id: Protocol identifier for the message
+ * @tx_size: transmit message size
+ * @rx_size: receive message size
+ * @p: pointer to the allocated and initialised message
+ *
+ * This function allocates the message using @scmi_one_xfer_get and
+ * initialise the header.
+ *
+ * Return: 0 if all went fine with @p pointing to message, else
+ *	corresponding error.
+ */
+int scmi_one_xfer_init(struct scmi_handle *handle, u8 msg_id, u8 msg_prot_id,
+		       size_t tx_size, size_t rx_size, struct scmi_xfer **p)
+{
+	int ret;
+	struct scmi_xfer *xfer;
+	struct scmi_info *info = handle_to_scmi_info(handle);
+	struct device *dev = info->dev;
+
+	/* Ensure we have sane transfer sizes */
+	if (rx_size > info->desc->max_msg_size ||
+	    tx_size > info->desc->max_msg_size)
+		return -ERANGE;
+
+	xfer = scmi_one_xfer_get(handle);
+	if (IS_ERR(xfer)) {
+		ret = PTR_ERR(xfer);
+		dev_err(dev, "failed to get free message slot(%d)\n", ret);
+		return ret;
+	}
+
+	xfer->tx.len = tx_size;
+	xfer->rx.len = rx_size ? : info->desc->max_msg_size;
+	xfer->hdr.id = msg_id;
+	xfer->hdr.protocol_id = msg_prot_id;
+
+	*p = xfer;
+	return 0;
+}
+
+/**
+ * scmi_handle_get() - Get the  SCMI handle for a device
+ *
+ * @dev: pointer to device for which we want SCMI handle
+ *
+ * NOTE: The function does not track individual clients of the framework
+ * and is expected to be maintained by caller of  SCMI protocol library.
+ * scmi_put_handle must be balanced with successful scmi_handle_get
+ *
+ * Return: pointer to handle if successful, else:
+ *	-EPROBE_DEFER if the instance is not ready
+ *	-ENODEV if the required node handler is missing
+ *	-EINVAL if invalid conditions are encountered.
+ */
+const struct scmi_handle *scmi_handle_get(struct device *dev)
+{
+	struct list_head *p;
+	struct scmi_info *info;
+	struct device_node *scmi_np;
+	struct scmi_handle *handle = NULL;
+
+	if (!dev) {
+		pr_err("missing device pointer\n");
+		return ERR_PTR(-EINVAL);
+	}
+	scmi_np = of_get_parent(dev->of_node);
+	if (!scmi_np) {
+		dev_err(dev, "no OF information\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	mutex_lock(&scmi_list_mutex);
+	list_for_each(p, &scmi_list) {
+		info = list_entry(p, struct scmi_info, node);
+		if (scmi_np == info->dev->of_node) {
+			handle = &info->handle;
+			info->users++;
+			break;
+		}
+	}
+	mutex_unlock(&scmi_list_mutex);
+	of_node_put(scmi_np);
+
+	if (!handle)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	return handle;
+}
+EXPORT_SYMBOL_GPL(scmi_handle_get);
+
+/**
+ * scmi_put_handle() - Release the handle acquired by scmi_handle_get
+ *
+ * @handle: handle acquired by scmi_handle_get
+ *
+ * NOTE: The function does not track individual clients of the framework
+ * and is expected to be maintained by caller of  SCMI protocol library.
+ * scmi_put_handle must be balanced with successful scmi_handle_get
+ *
+ * Return: 0 is successfully released
+ *	if an error pointer was passed, it returns the error value back,
+ *	if null was passed, it returns -EINVAL;
+ */
+int scmi_put_handle(const struct scmi_handle *handle)
+{
+	struct scmi_info *info;
+
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+	if (!handle)
+		return -EINVAL;
+
+	info = handle_to_scmi_info(handle);
+	mutex_lock(&scmi_list_mutex);
+	if (!WARN_ON(!info->users))
+		info->users--;
+	mutex_unlock(&scmi_list_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(scmi_put_handle);
+
+static void devm_scmi_release(struct device *dev, void *res)
+{
+	const struct scmi_handle **ptr = res;
+	const struct scmi_handle *handle = *ptr;
+	int ret;
+
+	ret = scmi_put_handle(handle);
+	if (ret)
+		dev_err(dev, "failed to put handle %d\n", ret);
+}
+
+/**
+ * devm_scmi_handle_get() - Managed get handle
+ * @dev: device for which we want SCMI handle for.
+ *
+ * NOTE: This releases the handle once the device resources are
+ * no longer needed. MUST NOT BE released with scmi_put_handle.
+ * The function does not track individual clients of the framework
+ * and is expected to be maintained by caller of  SCMI protocol library.
+ *
+ * Return: 0 if all went fine, else corresponding error.
+ */
+const struct scmi_handle *devm_scmi_handle_get(struct device *dev)
+{
+	const struct scmi_handle **ptr;
+	const struct scmi_handle *handle;
+
+	ptr = devres_alloc(devm_scmi_release, sizeof(*ptr), GFP_KERNEL);
+	if (!ptr)
+		return ERR_PTR(-ENOMEM);
+	handle = scmi_handle_get(dev);
+
+	if (!IS_ERR(handle)) {
+		*ptr = handle;
+		devres_add(dev, ptr);
+	} else {
+		devres_free(ptr);
+	}
+
+	return handle;
+}
+EXPORT_SYMBOL_GPL(devm_scmi_handle_get);
+
+static const struct scmi_desc scmi_generic_desc = {
+	.max_rx_timeout_ms = 30,	/* we may increase this if required */
+	.max_msg = 20,		/* Limited by MBOX_TX_QUEUE_LEN */
+	.max_msg_size = 128,
+};
+
+/* Each compatible listed below must have descriptor associated with it */
+static const struct of_device_id scmi_of_match[] = {
+	{ .compatible = "arm,scmi", .data = &scmi_generic_desc },
+	{ /* Sentinel */ },
+};
+
+MODULE_DEVICE_TABLE(of, scmi_of_match);
+
+static int scmi_xfer_info_init(struct scmi_info *sinfo)
+{
+	int i;
+	struct scmi_xfer *xfer;
+	struct device *dev = sinfo->dev;
+	const struct scmi_desc *desc = sinfo->desc;
+	struct scmi_xfers_info *info = &sinfo->minfo;
+
+	/* Pre-allocated messages, no more than what hdr.seq can support */
+	if (WARN_ON(desc->max_msg >= (MSG_TOKEN_ID_MASK + 1))) {
+		dev_err(dev, "Maximum message of %d exceeds supported %d\n",
+			desc->max_msg, MSG_TOKEN_ID_MASK + 1);
+		return -EINVAL;
+	}
+
+	info->xfer_block = devm_kcalloc(dev, desc->max_msg,
+					sizeof(*info->xfer_block), GFP_KERNEL);
+	if (!info->xfer_block)
+		return -ENOMEM;
+
+	info->xfer_alloc_table = devm_kcalloc(dev, BITS_TO_LONGS(desc->max_msg),
+					      sizeof(long), GFP_KERNEL);
+	if (!info->xfer_alloc_table)
+		return -ENOMEM;
+
+	bitmap_zero(info->xfer_alloc_table, desc->max_msg);
+
+	/* Pre-initialize the buffer pointer to pre-allocated buffers */
+	for (i = 0, xfer = info->xfer_block; i < desc->max_msg; i++, xfer++) {
+		xfer->rx.buf = devm_kcalloc(dev, sizeof(*xfer->rx.buf),
+					    desc->max_msg_size, GFP_KERNEL);
+		if (!xfer->rx.buf)
+			return -ENOMEM;
+
+		xfer->tx.buf = xfer->rx.buf;
+		init_completion(&xfer->done);
+	}
+
+	spin_lock_init(&info->xfer_lock);
+
+	sema_init(&info->sem_xfer_count, desc->max_msg);
+
+	return 0;
+}
+
+static int scmi_probe(struct platform_device *pdev)
+{
+	int ret = -EINVAL;
+	struct resource res;
+	resource_size_t size;
+	struct mbox_client *cl;
+	struct scmi_handle *handle;
+	const struct scmi_desc *desc;
+	struct scmi_info *info = NULL;
+	struct device *dev = &pdev->dev;
+	struct device_node *shmem, *np = dev->of_node;
+
+	desc = of_match_device(scmi_of_match, dev)->data;
+
+	info = devm_kzalloc(dev, sizeof(*info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	info->dev = dev;
+	info->desc = desc;
+	INIT_LIST_HEAD(&info->node);
+
+	ret = scmi_xfer_info_init(info);
+	if (ret)
+		return ret;
+
+	platform_set_drvdata(pdev, info);
+
+	cl = &info->cl;
+	cl->dev = dev;
+	cl->rx_callback = scmi_rx_callback;
+	cl->tx_prepare = scmi_tx_prepare;
+	cl->tx_block = false;
+	cl->knows_txdone = true;
+
+	shmem = of_parse_phandle(np, "shmem", 0);
+	ret = of_address_to_resource(shmem, 0, &res);
+	of_node_put(shmem);
+	if (ret) {
+		dev_err(dev, "failed to get SCMI Tx payload mem resource\n");
+		return ret;
+	}
+
+	size = resource_size(&res);
+	info->tx_payload = devm_ioremap(dev, res.start, size);
+	if (!info->tx_payload) {
+		dev_err(dev, "failed to ioremap SCMI Tx payload\n");
+		ret = -EADDRNOTAVAIL;
+		return ret;
+	}
+
+	info->tx_chan = mbox_request_channel_byname(cl, "tx");
+	if (IS_ERR(info->tx_chan)) {
+		ret = PTR_ERR(info->tx_chan);
+		goto out;
+	}
+
+	handle = &info->handle;
+	handle->dev = info->dev;
+
+	mutex_lock(&scmi_list_mutex);
+	list_add_tail(&info->node, &scmi_list);
+	mutex_unlock(&scmi_list_mutex);
+
+	return of_platform_populate(dev->of_node, NULL, NULL, dev);
+out:
+	if (!IS_ERR(info->tx_chan))
+		mbox_free_channel(info->tx_chan);
+	return ret;
+}
+
+static int scmi_remove(struct platform_device *pdev)
+{
+	int ret = 0;
+	struct scmi_info *info = platform_get_drvdata(pdev);
+
+	of_platform_depopulate(&pdev->dev);
+
+	mutex_lock(&scmi_list_mutex);
+	if (info->users)
+		ret = -EBUSY;
+	else
+		list_del(&info->node);
+	mutex_unlock(&scmi_list_mutex);
+
+	if (!ret)
+		/* Safe to free channels since no more users */
+		mbox_free_channel(info->tx_chan);
+
+	return ret;
+}
+
+static struct platform_driver scmi_driver = {
+	.driver = {
+		   .name = "arm-scmi",
+		   .of_match_table = of_match_ptr(scmi_of_match),
+		   },
+	.probe = scmi_probe,
+	.remove = scmi_remove,
+};
+
+module_platform_driver(scmi_driver);
+
+MODULE_ALIAS("platform: arm-scmi");
+MODULE_AUTHOR("Sudeep Holla <sudeep.holla@....com>");
+MODULE_DESCRIPTION("ARM SCMI protocol driver");
+MODULE_LICENSE("GPL v2");
diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
new file mode 100644
index 000000000000..0c795a765110
--- /dev/null
+++ b/include/linux/scmi_protocol.h
@@ -0,0 +1,48 @@
+/*
+ * SCMI Message Protocol driver header
+ *
+ * Copyright (C) 2017 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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/>.
+ */
+#include <linux/types.h>
+
+/**
+ * struct scmi_handle - Handle returned to ARM SCMI clients for usage.
+ *
+ * @dev: pointer to the SCMI device
+ */
+struct scmi_handle {
+	struct device *dev;
+};
+
+#if IS_REACHABLE(CONFIG_ARM_SCMI_PROTOCOL)
+int scmi_put_handle(const struct scmi_handle *handle);
+const struct scmi_handle *scmi_handle_get(struct device *dev);
+const struct scmi_handle *devm_scmi_handle_get(struct device *dev);
+#else
+static inline int scmi_put_handle(const struct scmi_handle *handle)
+{
+	return 0;
+}
+
+static inline const struct scmi_handle *scmi_handle_get(struct device *dev)
+{
+	return NULL;
+}
+
+static inline const struct scmi_handle *devm_scmi_handle_get(struct device *dev)
+{
+	return NULL;
+}
+#endif /* CONFIG_ARM_SCMI_PROTOCOL */
-- 
2.7.4

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