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    Subject[PATCH v4 12/16] firmware: arm_scmi: Add message passing abstractions for transports
    Date
    From: Peter Hilber <peter.hilber@opensynergy.com>

    Add abstractions for future transports using message passing, such as
    virtio. Derive the abstractions from the shared memory abstractions.

    Abstract the transport SDU through the opaque struct scmi_msg_payld.
    Also enable the transport to determine all other required information
    about the transport SDU.

    Signed-off-by: Peter Hilber <peter.hilber@opensynergy.com>
    ---
    drivers/firmware/Kconfig | 8 +-
    drivers/firmware/arm_scmi/Makefile | 1 +
    drivers/firmware/arm_scmi/common.h | 15 ++++
    drivers/firmware/arm_scmi/msg.c | 113 +++++++++++++++++++++++++++++
    4 files changed, 136 insertions(+), 1 deletion(-)
    create mode 100644 drivers/firmware/arm_scmi/msg.c

    diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
    index 358f895847b5..e74d25065d07 100644
    --- a/drivers/firmware/Kconfig
    +++ b/drivers/firmware/Kconfig
    @@ -9,7 +9,7 @@ menu "Firmware Drivers"
    config ARM_SCMI_PROTOCOL
    tristate "ARM System Control and Management Interface (SCMI) Message Protocol"
    depends on ARM || ARM64 || COMPILE_TEST
    - depends on ARM_SCMI_HAVE_SHMEM
    + depends on ARM_SCMI_HAVE_SHMEM || ARM_SCMI_HAVE_MSG
    help
    ARM System Control and Management Interface (SCMI) protocol is a
    set of operating system-independent software interfaces that are
    @@ -33,6 +33,12 @@ config ARM_SCMI_HAVE_SHMEM
    This declares whether a shared memory based transport for SCMI is
    available.

    +config ARM_SCMI_HAVE_MSG
    + bool
    + help
    + This declares whether a message passing based transport for SCMI is
    + available.
    +
    config ARM_SCMI_POWER_DOMAIN
    tristate "SCMI power domain driver"
    depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
    diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
    index 5a2d4c32e0ae..f6b4acb8abdb 100644
    --- a/drivers/firmware/arm_scmi/Makefile
    +++ b/drivers/firmware/arm_scmi/Makefile
    @@ -4,6 +4,7 @@ scmi-driver-y = driver.o notify.o
    scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
    scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
    scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
    +scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
    scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
    scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
    $(scmi-transport-y)
    diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
    index b783ae058c8a..fa4075336580 100644
    --- a/drivers/firmware/arm_scmi/common.h
    +++ b/drivers/firmware/arm_scmi/common.h
    @@ -410,6 +410,21 @@ void shmem_clear_channel(struct scmi_shared_mem __iomem *shmem);
    bool shmem_poll_done(struct scmi_shared_mem __iomem *shmem,
    struct scmi_xfer *xfer);

    +/* declarations for message passing transports */
    +struct scmi_msg_payld;
    +
    +/** Maximum overhead of message w.r.t. struct scmi_desc.max_msg_size */
    +#define SCMI_MSG_MAX_PROT_OVERHEAD (2 * sizeof(__le32))
    +
    +size_t msg_response_size(struct scmi_xfer *xfer);
    +size_t msg_command_size(struct scmi_xfer *xfer);
    +void msg_tx_prepare(struct scmi_msg_payld *msg, struct scmi_xfer *xfer);
    +u32 msg_read_header(struct scmi_msg_payld *msg);
    +void msg_fetch_response(struct scmi_msg_payld *msg, size_t len,
    + struct scmi_xfer *xfer);
    +void msg_fetch_notification(struct scmi_msg_payld *msg, size_t len,
    + size_t max_len, struct scmi_xfer *xfer);
    +
    void scmi_notification_instance_data_set(const struct scmi_handle *handle,
    void *priv);
    void *scmi_notification_instance_data_get(const struct scmi_handle *handle);
    diff --git a/drivers/firmware/arm_scmi/msg.c b/drivers/firmware/arm_scmi/msg.c
    new file mode 100644
    index 000000000000..8a2d3303d281
    --- /dev/null
    +++ b/drivers/firmware/arm_scmi/msg.c
    @@ -0,0 +1,113 @@
    +// SPDX-License-Identifier: GPL-2.0
    +/*
    + * For transports using message passing.
    + *
    + * Derived from shm.c.
    + *
    + * Copyright (C) 2019 ARM Ltd.
    + * Copyright (C) 2020 OpenSynergy GmbH
    + */
    +
    +#include <linux/io.h>
    +#include <linux/processor.h>
    +#include <linux/types.h>
    +
    +#include "common.h"
    +
    +/*
    + * struct scmi_msg_payld - Transport SDU layout
    + *
    + * The SCMI specification requires all parameters, message headers, return
    + * arguments or any protocol data to be expressed in little endian format only.
    + */
    +struct scmi_msg_payld {
    + __le32 msg_header;
    + __le32 msg_payload[];
    +};
    +
    +/**
    + * msg_command_size() - Actual size of transport SDU for command.
    + *
    + * @xfer: message which core has prepared for sending
    + *
    + * Return: transport SDU size.
    + */
    +size_t msg_command_size(struct scmi_xfer *xfer)
    +{
    + return sizeof(struct scmi_msg_payld) + xfer->tx.len;
    +}
    +
    +/**
    + * msg_response_size() - Maximum size of transport SDU for response.
    + *
    + * @xfer: message which core has prepared for sending
    + *
    + * Return: transport SDU size.
    + */
    +size_t msg_response_size(struct scmi_xfer *xfer)
    +{
    + return sizeof(struct scmi_msg_payld) + sizeof(__le32) + xfer->rx.len;
    +}
    +
    +/**
    + * msg_tx_prepare() - Set up transport SDU for command.
    + *
    + * @msg: transport SDU for command
    + * @xfer: message which is being sent
    + */
    +void msg_tx_prepare(struct scmi_msg_payld *msg, struct scmi_xfer *xfer)
    +{
    + msg->msg_header = cpu_to_le32(pack_scmi_header(&xfer->hdr));
    + if (xfer->tx.buf)
    + memcpy(msg->msg_payload, xfer->tx.buf, xfer->tx.len);
    +}
    +
    +/**
    + * msg_read_header() - Read SCMI header from transport SDU.
    + *
    + * @msg: transport SDU
    + *
    + * Return: SCMI header
    + */
    +u32 msg_read_header(struct scmi_msg_payld *msg)
    +{
    + return le32_to_cpu(msg->msg_header);
    +}
    +
    +/**
    + * msg_fetch_response() - Fetch response SCMI payload from transport SDU.
    + *
    + * @msg: transport SDU with response
    + * @len: transport SDU size
    + * @xfer: message being responded to
    + */
    +void msg_fetch_response(struct scmi_msg_payld *msg, size_t len,
    + struct scmi_xfer *xfer)
    +{
    + size_t prefix_len = sizeof(*msg) + sizeof(msg->msg_payload[0]);
    +
    + xfer->hdr.status = le32_to_cpu(msg->msg_payload[0]);
    + xfer->rx.len = min_t(size_t, xfer->rx.len,
    + len >= prefix_len ? len - prefix_len : 0);
    +
    + /* Take a copy to the rx buffer.. */
    + memcpy(xfer->rx.buf, &msg->msg_payload[1], xfer->rx.len);
    +}
    +
    +/**
    + * msg_fetch_notification() - Fetch notification payload from transport SDU.
    + *
    + * @msg: transport SDU with notification
    + * @len: transport SDU size
    + * @max_len: maximum SCMI payload size to fetch
    + * @xfer: notification message
    + */
    +void msg_fetch_notification(struct scmi_msg_payld *msg, size_t len,
    + size_t max_len, struct scmi_xfer *xfer)
    +{
    + xfer->rx.len = min_t(size_t, max_len,
    + len >= sizeof(*msg) ? len - sizeof(*msg) : 0);
    +
    + /* Take a copy to the rx buffer.. */
    + memcpy(xfer->rx.buf, msg->msg_payload, xfer->rx.len);
    +}
    --
    2.17.1
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