Hi,
On Fri, Jul 11, 2025 at 4:49 PM <abdellatif.elkhl...@arm.com> wrote:
>
> From: Abdellatif El Khlifi <abdellatif.elkhl...@arm.com>
>
> Add to the FF-A bus FFA_MEM_SHARE ABI
>
> The FFA_MEM_SHARE is a memory management ABI described in the FF-A v1.0
> specification [1].
>
> This ABI starts a transaction to grant access to a memory region
> to one or more Borrowers (aka Secure Partitions or endpoints).
>
> This work is based on the implementation in Linux kernel [2].
>
> [1]: https://developer.arm.com/documentation/den0077/a/?lang=en
> [2]: commit cc2195fe536c28e192df5d07e6dd277af36814b4
> Files: drivers/firmware/arm_ffa/driver.c , include/linux/arm_ffa.h
>
> Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhl...@arm.com>
> Cc: Tom Rini <tr...@konsulko.com>
> Cc: Simon Glass <s...@chromium.org>
> Cc: Ilias Apalodimas <ilias.apalodi...@linaro.org>
> Cc: Jens Wiklander <jens.wiklan...@linaro.org>
> Cc: Casey Connolly <casey.conno...@linaro.org>
> Cc: Heinrich Schuchardt <heinrich.schucha...@canonical.com>
>
> ---
>
> Changelog of changes:
> ===========================
>
> v2:
>
> * As suggested by Heinrich: The ops NULL check removed
>
> v1:
>
> * Add FFA_MEM_SHARE support
>
> doc/arch/arm64.ffa.rst | 2 +
> drivers/firmware/arm-ffa/arm-ffa-uclass.c | 210 ++++++++++++++++++++++
> drivers/firmware/arm-ffa/arm-ffa.c | 3 +-
> include/arm_ffa.h | 86 ++++++++-
> include/arm_ffa_priv.h | 142 ++++++++++++++-
> 5 files changed, 439 insertions(+), 4 deletions(-)
>
> diff --git a/doc/arch/arm64.ffa.rst b/doc/arch/arm64.ffa.rst
> index f966f8ba6af..3eec735d741 100644
> --- a/doc/arch/arm64.ffa.rst
> +++ b/doc/arch/arm64.ffa.rst
> @@ -185,6 +185,7 @@ The following features are provided:
> - FFA_INTERRUPT
> - FFA_MSG_SEND_DIRECT_REQ
> - FFA_MSG_SEND_DIRECT_RESP
> + - FFA_MEM_SHARE
>
> - Support for the 64-bit version of the following ABIs:
>
> @@ -203,6 +204,7 @@ The following features are provided:
> - ffa_partition_info_get
> - ffa_sync_send_receive
> - ffa_rxtx_unmap
> + - ffa_memory_share
>
> - FF-A bus discovery makes sure FF-A framework is responsive and compatible
> with the driver
> diff --git a/drivers/firmware/arm-ffa/arm-ffa-uclass.c
> b/drivers/firmware/arm-ffa/arm-ffa-uclass.c
> index 32dd9458da9..9af574760d2 100644
> --- a/drivers/firmware/arm-ffa/arm-ffa-uclass.c
> +++ b/drivers/firmware/arm-ffa/arm-ffa-uclass.c
> @@ -95,6 +95,20 @@ static struct ffa_abi_errmap err_msg_map[FFA_ERRMAP_COUNT]
> = {
> "DENIED: Buffer pair already registered",
> },
> },
> + [FFA_ID_TO_ERRMAP_ID(FFA_MEM_SHARE)] = {
> + {
> + [ABORTED] =
> + "ABORTED: Failure in the transmission of fragments or
> in time slicing",
> + [INVALID_PARAMETERS] =
> + "INVALID_PARAMETERS: Validation failed for the Memory
> Transaction or the Endpoint memory access descriptor",
> + [NO_MEMORY] =
> + "NO_MEMORY: Insufficient memory to complete this
> operation",
> + [BUSY] =
> + "BUSY: The TX buffer is busy",
> + [DENIED] =
> + "DENIED: Memory region ownership, permission, access
> or attributes error",
> + },
> + },
> };
>
> /**
> @@ -929,6 +943,177 @@ int ffa_msg_send_direct_req_hdlr(struct udevice *dev,
> u16 dst_part_id,
> return ffa_to_std_errno(ffa_errno);
> }
>
> +/**
> + * ffa_mem_desc_offset() - helper for descriptors offset calculation
> + * @count: An integer defining the number of Endpoint memory access
> descriptors
> + *
> + * Calculate the offset of the Endpoint memory access descriptor and
> + * the Composite memory region descriptor.
> + *
> + * Return:
> + *
> + * The descriptor offset.
> + */
> +static inline u32 ffa_mem_desc_offset(int count)
"inline" doesn't make much difference in a .c file.
> +{
> + u32 offset = count * sizeof(struct ffa_mem_region_attributes);
> +
> + offset += sizeof(struct ffa_mem_region);
> +
> + return offset;
> +}
> +
> +/**
> + * ffa_setup_and_transmit() - set up the memory and transmit data using FF-A
> + * @dev: The FF-A bus device
> + * @func_id: An integer identifying the function
> + * @buffer: A pointer to the data to be transmitted (FF-A TX buffer)
> + * @args: A pointer to a structure containing additional user arguments
> + *
> + * Setup the memory transaction related to the access to a specified
> + * memory region.
> + * Currently we support FFA_MEM_SHARE only.
> + *
> + * Return:
> + *
> + * 0 on success. . Otherwise, failure
> + */
> +static int ffa_setup_and_transmit(struct udevice *dev, u32 func_id,
> + void *buffer, struct ffa_mem_ops_args *args)
> +{
> + ffa_value_t res = {0};
> + int ffa_errno;
> + u32 composite_offset;
> + u32 total_length;
> + struct ffa_mem_region *mem_region = buffer;
> + struct ffa_composite_mem_region *composite;
> + struct ffa_mem_region_addr_range *constituent;
> + struct ffa_mem_region_attributes *ep_mem_access;
> + u32 idx;
> + struct ffa_priv *uc_priv;
> +
> + uc_priv = dev_get_uclass_priv(dev);
> +
> + mem_region->tag = args->tag;
> + mem_region->flags = args->flags;
> + mem_region->sender_id = uc_priv->id;
> +
> + /*
> + * These attributes are only valid for FFA_MEM_SHARE.
> + * They are not valid for FFA_MEM_LEND (no implemented).
> + */
> + if (func_id == FFA_MEM_SHARE)
> + mem_region->attributes = FFA_MEM_NORMAL | FFA_MEM_WRITE_BACK
> + | FFA_MEM_INNER_SHAREABLE;
> + else
> + mem_region->attributes = 0;
> +
> + mem_region->handle = 0;
> + mem_region->ep_count = args->nattrs;
> + mem_region->reserved1 = 0;
> + mem_region->reserved2 = 0;
> +
> + ep_mem_access = buffer + ffa_mem_desc_offset(0);
> +
> + composite_offset = ffa_mem_desc_offset(args->nattrs);
> +
> + /* Multiple borrowers supported */
> + for (idx = 0; idx < args->nattrs; idx++, ep_mem_access++) {
> + ep_mem_access->receiver = args->attrs[idx].receiver;
> + ep_mem_access->attrs = args->attrs[idx].attrs;
> + ep_mem_access->composite_off = composite_offset;
> + ep_mem_access->flag = 0;
> + ep_mem_access->reserved = 0;
> + }
> +
> + /* Only one Composite and one Constituent memory region supported */
> + composite = buffer + composite_offset;
> + composite->total_pg_cnt = args->pg_cnt;
> + composite->addr_range_cnt = FFA_MEM_CONSTITUENTS;
> + composite->reserved = 0;
> +
> + constituent = &composite->constituents[0];
> + constituent->address = map_to_sysmem(args->address);
> + constituent->pg_cnt = args->pg_cnt;
> + constituent->reserved = 0;
> +
> + total_length = composite_offset + sizeof(*composite) +
> + sizeof(*constituent);
> +
> + /*
> + * Note: Time slicing is not supported.
> + * It's only available to EL1 and S-EL1 endpoints.
> + */
Isn't U-Boot an EL1 endpoint?
> +
> + invoke_ffa_fn((ffa_value_t){
> + .a0 = FFA_SMC_32(func_id),
> + .a1 = total_length,
> + .a2 = total_length,
> + .a3 = 0, /* the TX buffer is used */
> + .a4 = 0, /* the TX buffer is used */
> + },
> + &res
> + );
> +
> + if (res.a0 != FFA_SMC_32(FFA_SUCCESS)) {
> + ffa_errno = res.a2;
> + ffa_print_error_log(func_id, ffa_errno);
> + return ffa_to_std_errno(ffa_errno);
> + }
> +
> + args->g_handle = PACK_HANDLE(res.a2, res.a3);
> + return 0;
> +}
> +
> +/**
> + * ffa_memory_ops() - wrapper for the memory management ABIs
> + * @dev: The FF-A bus device
> + * @func_id: An integer identifying the function
> + * @args: A pointer to a structure containing additional user arguments
> + *
> + * Verify the use of the TX buffer then call ffa_setup_and_transmit().
> + * Currently we support FFA_MEM_SHARE only.
> + *
> + * Return:
> + *
> + * 0 on success. Otherwise, failure
> + */
> +static int ffa_memory_ops(struct udevice *dev, u32 func_id,
> + struct ffa_mem_ops_args *args)
> +{
> + void *buffer;
> + struct ffa_priv *uc_priv = dev_get_uclass_priv(dev);
> +
> + if (!args->use_txbuf) {
> + log_err("only TX buffer supported\n");
> + return -EPROTONOSUPPORT;
> + }
> +
> + buffer = uc_priv->pair.txbuf;
> +
> + if (!buffer || !args->attrs || !args->address)
> + return -EINVAL;
> +
> + return ffa_setup_and_transmit(dev, func_id, buffer, args);
> +}
> +
> +/**
> + * ffa_memory_share_hdlr() - FFA_MEM_SHARE handler function
> + * @dev: The FF-A bus device
> + * @args: A pointer to a structure containing additional user arguments
> + *
> + * Implement FFA_MEM_SHARE FF-A function
> + * to grant access to a memory region to one or more Borrowers.
> + *
> + * Return:
> + *
> + * 0 on success. Otherwise, failure
> + */
> +int ffa_memory_share_hdlr(struct udevice *dev, struct ffa_mem_ops_args *args)
> +{
> + return ffa_memory_ops(dev, FFA_MEM_SHARE, args);
> +}
> +
> /* FF-A driver operations (used by clients for communicating with FF-A)*/
>
> /**
> @@ -1006,6 +1191,31 @@ int ffa_rxtx_unmap(struct udevice *dev)
> return ops->rxtx_unmap(dev);
> }
>
> +/**
> + * ffa_memory_share() - FFA_MEM_SHARE driver operation
> + * @dev: The FF-A bus device
> + * @args: A pointer to a structure containing additional user arguments
> + *
> + * Driver operation for FFA_MEM_SHARE.
> + * Please see ffa_memory_share_hdlr() description for more details.
> + *
> + * Return:
> + *
> + * 0 on success. Otherwise, failure
> + */
> +int ffa_memory_share(struct udevice *dev, struct ffa_mem_ops_args *args)
> +{
> + struct ffa_bus_ops *ops = ffa_get_ops(dev);
> +
> + if (!args)
> + return -EINVAL;
> +
> + if (!ops->memory_share)
> + return -ENOSYS;
> +
> + return ops->memory_share(dev, args);
> +}
> +
> /**
> * ffa_do_probe() - probing FF-A framework
> * @dev: the FF-A bus device (arm_ffa)
> diff --git a/drivers/firmware/arm-ffa/arm-ffa.c
> b/drivers/firmware/arm-ffa/arm-ffa.c
> index 94e6105cb38..df904cae412 100644
> --- a/drivers/firmware/arm-ffa/arm-ffa.c
> +++ b/drivers/firmware/arm-ffa/arm-ffa.c
> @@ -1,6 +1,6 @@
> // SPDX-License-Identifier: GPL-2.0+
> /*
> - * Copyright 2022-2023 Arm Limited and/or its affiliates
> <open-source-off...@arm.com>
> + * Copyright 2022-2023, 2025 Arm Limited and/or its affiliates
> <open-source-off...@arm.com>
> *
> * Authors:
> * Abdellatif El Khlifi <abdellatif.elkhl...@arm.com>
> @@ -84,6 +84,7 @@ static const struct ffa_bus_ops ffa_ops = {
> .partition_info_get = ffa_get_partitions_info_hdlr,
> .sync_send_receive = ffa_msg_send_direct_req_hdlr,
> .rxtx_unmap = ffa_unmap_rxtx_buffers_hdlr,
> + .memory_share = ffa_memory_share_hdlr,
> };
>
> /* Registering the FF-A driver as an SMCCC feature driver */
> diff --git a/include/arm_ffa.h b/include/arm_ffa.h
> index 2994d8ee3ae..b91b0279371 100644
> --- a/include/arm_ffa.h
> +++ b/include/arm_ffa.h
> @@ -1,6 +1,6 @@
> /* SPDX-License-Identifier: GPL-2.0+ */
> /*
> - * Copyright 2022-2023 Arm Limited and/or its affiliates
> <open-source-off...@arm.com>
> + * Copyright 2022-2023, 2025 Arm Limited and/or its affiliates
> <open-source-off...@arm.com>
> *
> * Authors:
> * Abdellatif El Khlifi <abdellatif.elkhl...@arm.com>
> @@ -81,11 +81,74 @@ struct ffa_send_direct_data {
>
> struct udevice;
>
> +/**
> + * struct ffa_mem_region_attributes - Endpoint memory access descriptor
> + *
> + * The data structure used in memory management transactions to create an
> + * association between an endpoint, memory access permissions and a composite
> + * memory region description.
> + *
> + * For more details, please refer to Table 5.16 and Table 5.15 in the FF-A
> + * specification v1.0.
> + *
> + * This structure was taken from Linux.
> + */
> +struct ffa_mem_region_attributes {
> + /* The ID of the VM to which the memory is being given or shared. */
> + u16 receiver;
> + /*
> + * The permissions with which the memory region should be mapped in
> the
> + * receiver's page table.
> + */
> +#define FFA_MEM_EXEC BIT(3)
> +#define FFA_MEM_NO_EXEC BIT(2)
> +#define FFA_MEM_RW BIT(1)
> +#define FFA_MEM_RO BIT(0)
> + u8 attrs;
> + /*
> + * Flags used during FFA_MEM_RETRIEVE_REQ and FFA_MEM_RETRIEVE_RESP
> + * for memory regions with multiple borrowers.
> + */
> +#define FFA_MEM_RETRIEVE_SELF_BORROWER BIT(0)
> + u8 flag;
> + /*
> + * Offset in bytes from the start of the outer `ffa_memory_region` to
> + * an `struct ffa_mem_region_addr_range`.
> + */
> + u32 composite_off;
> + u64 reserved;
> +};
> +
> +/**
> + * struct ffa_mem_ops_args - User arguments to the memory management ABIs
> + * @use_txbuf: Whether to use the TX buffer for the memory transaction
> + * @nattrs: Number of the borrowers
> + * @flags: Memory transaction flags
> + * @tag: The tag associated with the transaction
> + * @g_handle: Globally unique Handle to identify the memory region (out)
> + * @address: Virtual address of the memory region
> + * @attrs: Memory access permissions of each borrower
> + *
> + * The structured filled by the user and passed to the memory
> + * management ABIs (e.g: FFA_MEM_SHARE)
> + */
> +struct ffa_mem_ops_args {
> + bool use_txbuf;
> + u32 nattrs;
> + u32 flags;
> + u64 tag;
> + u64 g_handle;
> + void *address;
> + u32 pg_cnt;
> + struct ffa_mem_region_attributes *attrs;
> +};
> +
> /**
> * struct ffa_bus_ops - Operations for FF-A
> * @partition_info_get: callback for the FFA_PARTITION_INFO_GET
> * @sync_send_receive: callback for the FFA_MSG_SEND_DIRECT_REQ
> * @rxtx_unmap: callback for the FFA_RXTX_UNMAP
> + * @memory_share: callback for the FFA_MEM_SHARE
> *
> * The data structure providing all the operations supported by the driver.
> * This structure is EFI runtime resident.
> @@ -97,6 +160,7 @@ struct ffa_bus_ops {
> struct ffa_send_direct_data *msg,
> bool is_smc64);
> int (*rxtx_unmap)(struct udevice *dev);
> + int (*memory_share)(struct udevice *dev, struct ffa_mem_ops_args
> *args);
> };
>
> #define ffa_get_ops(dev) ((struct ffa_bus_ops *)(dev)->driver->ops)
> @@ -196,6 +260,26 @@ int ffa_partition_info_get(struct udevice *dev, const
> char *uuid_str,
> int ffa_get_partitions_info_hdlr(struct udevice *dev, const char *uuid_str,
> u32 *sp_count, struct ffa_partition_desc
> **sp_descs);
>
> +/**
> + * ffa_memory_share() - FFA_MEM_SHARE driver operation
> + * Please see ffa_memory_share_hdlr() description for more details.
> + */
> +int ffa_memory_share(struct udevice *dev, struct ffa_mem_ops_args *args);
> +
> +/**
> + * ffa_memory_share_hdlr() - FFA_MEM_SHARE handler function
> + * @dev: The FF-A bus device
> + * @args: A pointer to a structure containing additional user arguments
> + *
> + * Implement FFA_MEM_SHARE FF-A function
> + * to grant access to a memory region to one or more Borrowers.
> + *
> + * Return:
> + *
> + * 0 on success. Otherwise, failure
> + */
> +int ffa_memory_share_hdlr(struct udevice *dev, struct ffa_mem_ops_args
> *args);
> +
> struct ffa_priv;
>
> /**
> diff --git a/include/arm_ffa_priv.h b/include/arm_ffa_priv.h
> index d564c33c647..a259911d5b9 100644
> --- a/include/arm_ffa_priv.h
> +++ b/include/arm_ffa_priv.h
> @@ -1,6 +1,6 @@
> /* SPDX-License-Identifier: GPL-2.0+ */
> /*
> - * Copyright 2022-2023 Arm Limited and/or its affiliates
> <open-source-off...@arm.com>
> + * Copyright 2022-2023, 2025 Arm Limited and/or its affiliates
> <open-source-off...@arm.com>
> *
> * Authors:
> * Abdellatif El Khlifi <abdellatif.elkhl...@arm.com>
> @@ -132,10 +132,11 @@ enum ffa_abis {
> FFA_RUN = 0x6d,
> FFA_MSG_SEND_DIRECT_REQ = 0x6f,
> FFA_MSG_SEND_DIRECT_RESP = 0x70,
> + FFA_MEM_SHARE = 0x73,
>
> /* To be updated when adding new FFA IDs */
> FFA_FIRST_ID = FFA_ERROR, /* Lowest number ID */
> - FFA_LAST_ID = FFA_MSG_SEND_DIRECT_RESP, /* Highest
> number ID */
> + FFA_LAST_ID = FFA_MEM_SHARE, /* Highest number ID */
> };
>
> enum ffa_abi_errcode {
> @@ -219,6 +220,143 @@ struct ffa_priv {
> struct ffa_rxtxpair pair;
> };
>
> +/* FF-A memory management ABIs data structures */
> +
> +/**
> + * struct ffa_mem_region - Lend, donate or share memory transaction
> descriptor
> + *
> + * Specifies the data structure that must be used by the Owner/Lender and a
> + * Borrower/Receiver in a transaction to donate, lend or share a memory
> region.
> + * It specifies the memory region description, properties and other
> transaction
> + * attributes in an invocation of the following ABIs.
> + *
> + * FFA_MEM_DONATE.
> + * FFA_MEM_LEND.
> + * FFA_MEM_SHARE.
> + * FFA_MEM_RETRIEVE_REQ.
> + * FFA_MEM_RETRIEVE_RESP.
> + *
> + * For more details, please refer to the Table 5.19 in the FF-A specification
> + * v1.0.
> + *
> + * The interpretation of some fields depends on the ABI this structure is
> used
> + * with. This variance in behavior is also specified in the Table 5.19.
> + *
> + * This structure was taken from Linux and adapted to FF-A v1.0.
> + */
> +struct ffa_mem_region {
> + /* The ID of the VM/owner which originally sent the memory region */
> + u16 sender_id;
> +#define FFA_MEM_NORMAL BIT(5)
> +#define FFA_MEM_DEVICE BIT(4)
> +
> +#define FFA_MEM_WRITE_BACK (3 << 2)
> +#define FFA_MEM_NON_CACHEABLE BIT(2)
> +
> +#define FFA_DEV_nGnRnE (0 << 2)
> +#define FFA_DEV_nGnRE BIT(2)
Prefer (1 << 2) here. That's also what's used in the kernel code.
> +#define FFA_DEV_nGRE (2 << 2)
> +#define FFA_DEV_GRE (3 << 2)
> +
> +#define FFA_MEM_NON_SHAREABLE (0)
> +#define FFA_MEM_OUTER_SHAREABLE (2)
> +#define FFA_MEM_INNER_SHAREABLE (3)
> + /* Memory region attributes */
> + u8 attributes;
> +
> + u8 reserved1;
> +
> +/*
> + * Clear memory region contents after unmapping it from the sender and
> + * before mapping it for any receiver.
> + */
> +#define FFA_MEM_CLEAR BIT(0)
> +/*
> + * Whether the hypervisor may time slice the memory sharing or retrieval
> + * operation.
> + */
> +#define FFA_TIME_SLICE_ENABLE BIT(1)
> +
> +#define FFA_MEM_RETRIEVE_TYPE_IN_RESP (0 << 3)
> +#define FFA_MEM_RETRIEVE_TYPE_SHARE BIT(3)
Please use (1 << 3) for this value, like in the kernel.
Cheers,
Jens
> +#define FFA_MEM_RETRIEVE_TYPE_LEND (2 << 3)
> +#define FFA_MEM_RETRIEVE_TYPE_DONATE (3 << 3)
> +
> +#define FFA_MEM_RETRIEVE_ADDR_ALIGN_HINT BIT(9)
> +#define FFA_MEM_RETRIEVE_ADDR_ALIGN(x) ((x) << 5)
> + /* Flags to control behaviour of the transaction. */
> + u32 flags;
> +#define HANDLE_LOW_MASK GENMASK_ULL(31, 0)
> +#define HANDLE_HIGH_MASK GENMASK_ULL(63, 32)
> +#define HANDLE_LOW(x) ((u32)(FIELD_GET(HANDLE_LOW_MASK, (x))))
> +#define HANDLE_HIGH(x) ((u32)(FIELD_GET(HANDLE_HIGH_MASK,
> (x))))
> +
> +#define PACK_HANDLE(l, h) \
> + (FIELD_PREP(HANDLE_LOW_MASK, (l)) | FIELD_PREP(HANDLE_HIGH_MASK, (h)))
> + /*
> + * A globally-unique ID assigned by the hypervisor for a region
> + * of memory being sent between VMs.
> + */
> + u64 handle;
> + /*
> + * An implementation defined value associated with the receiver and
> the
> + * memory region.
> + */
> + u64 tag;
> +
> + u32 reserved2;
> +
> + /*
> + * The number of `ffa_mem_region_attributes` entries included in this
> + * transaction.
> + */
> + u32 ep_count;
> +};
> +
> +/**
> + * struct ffa_mem_region_addr_range - Constituent memory region descriptor
> + *
> + * Each descriptor specifies the base address and size of a virtually or
> + * physically contiguous memory region.
> + *
> + * For more details, please refer to Table 5.14 in the FF-A
> + * specification v1.0.
> + *
> + * This structure was taken from Linux.
> + */
> +struct ffa_mem_region_addr_range {
> + /* The base IPA of the constituent memory region, aligned to 4 kiB */
> + u64 address;
> + /* The number of 4 kiB pages in the constituent memory region. */
> + u32 pg_cnt;
> + u32 reserved;
> +};
> +
> +/**
> + * struct ffa_composite_mem_region - Composite memory region descriptor
> + *
> + * For more details, please refer to Table 5.13 in the FF-A
> + * specification v1.0.
> + *
> + * This structure was taken from Linux.
> + */
> +struct ffa_composite_mem_region {
> + /*
> + * The total number of 4 kiB pages included in this memory region.
> This
> + * must be equal to the sum of page counts specified in each
> + * `struct ffa_mem_region_addr_range`.
> + */
> + u32 total_pg_cnt;
> + /* The number of constituents included in this memory region range */
> +#define FFA_MEM_CONSTITUENTS (1)
> + u32 addr_range_cnt;
> + u64 reserved;
> + /** An array of `addr_range_cnt` memory region constituents. */
> + struct ffa_mem_region_addr_range constituents[];
> +};
> +
> +/* Functions prototypes */
> +
> /**
> * ffa_get_version_hdlr() - FFA_VERSION handler function
> * @dev: The FF-A bus device
> --
> 2.25.1
>
