Re: [PATCH v6 14/17] firmware: arm_scmi: Add message passing abstractions for transports

[Peter Hilber <peter.hilber@opensynergy.com>]

On 12.07.21 16:18, Cristian Marussi wrote:
> 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>
> [ Cristian: Adapted to new SCMI Kconfig layout, updated Copyrigths ]
> Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
> ---
> v4 --> v5
> - adapted to new SCMI Kconfig
> - removed raw_payload msg helpers
> v3 --> v4
> - added raw_payload msg helpers
> ---
>   drivers/firmware/arm_scmi/Kconfig  |   6 ++
>   drivers/firmware/arm_scmi/Makefile |   1 +
>   drivers/firmware/arm_scmi/common.h |  15 ++++
>   drivers/firmware/arm_scmi/msg.c    | 113 +++++++++++++++++++++++++++++
>   4 files changed, 135 insertions(+)
>   create mode 100644 drivers/firmware/arm_scmi/msg.c
> 
> diff --git a/drivers/firmware/arm_scmi/Kconfig b/drivers/firmware/arm_scmi/Kconfig
> index ee6517b24080..1fdaa8ad7d3f 100644
> --- a/drivers/firmware/arm_scmi/Kconfig
> +++ b/drivers/firmware/arm_scmi/Kconfig
> @@ -34,6 +34,12 @@ 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_TRANSPORT_MAILBOX
>   	bool "SCMI transport based on Mailbox"
>   	depends on ARM_SCMI_PROTOCOL && MAILBOX
> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> index e0e6bd3dba9e..aaad9f6589aa 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_ARM_SCMI_TRANSPORT_MAILBOX) += mailbox.o
>   scmi-transport-$(CONFIG_ARM_SCMI_TRANSPORT_SMC) += smc.o
> +scmi-transport-$(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 14457f0d5dea..7a1e84dc191b 100644
> --- a/drivers/firmware/arm_scmi/common.h
> +++ b/drivers/firmware/arm_scmi/common.h
> @@ -415,6 +415,21 @@ 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..639969b7dc10
> --- /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) 2019-2021 ARM Ltd.
> + * Copyright (C) 2020-2021 OpenSynergy GmbH
> + */
> +
> +#include <linux/io.h>
> +#include <linux/processor.h>

The above two includes appear to be unnecessary.

> +#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);
> +}
>