Re: [RFC PATCH 2/8] firmware: arm_scmi: add basic driver infrastructure for SCMI

[Roy Franz]

On Wed, Jun 7, 2017 at 9:10 AM, Sudeep Holla <sudeep.holla@xxxxxxx> wrote:
> 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@xxxxxxx>
> ---
>  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
> + */

nit:
This really has more to do with the SCMI protocol defining everything
as little endian,
rather the endian-ness of the SCP, right?  There could be SCP
implementations that
are not Cortex M3s or 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@xxxxxxx>");
> +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
>