FPGA Region

Overview

This document is meant to be a brief overview of the FPGA region API usage. A more conceptual look at regions can be found in the Device Tree binding document [1].

For the purposes of this API document, let’s just say that a region associates an FPGA Manager and a bridge (or bridges) with a reprogrammable region of an FPGA or the whole FPGA. The API provides a way to register a region and to program a region.

Currently the only layer above fpga-region.c in the kernel is the Device Tree support (of-fpga-region.c) described in [1]. The DT support layer uses regions to program the FPGA and then DT to handle enumeration. The common region code is intended to be used by other schemes that have other ways of accomplishing enumeration after programming.

An fpga-region can be set up to know the following things:

  • which FPGA manager to use to do the programming

  • which bridges to disable before programming and enable afterwards.

Additional info needed to program the FPGA image is passed in the struct fpga_image_info including:

  • pointers to the image as either a scatter-gather buffer, a contiguous buffer, or the name of firmware file

  • flags indicating specifics such as whether the image is for partial reconfiguration.

How to add a new FPGA region

An example of usage can be seen in the probe function of [2].

API to add a new FPGA region

Helper macros fpga_region_register() and fpga_region_register_full() automatically set the module that registers the FPGA region as the owner.

The FPGA region’s probe function will need to get a reference to the FPGA Manager it will be using to do the programming. This usually would happen during the region’s probe function.

The FPGA region will need to specify which bridges to control while programming the FPGA. The region driver can build a list of bridges during probe time (fpga_region->bridge_list) or it can have a function that creates the list of bridges to program just before programming (fpga_region->get_bridges). The FPGA bridge framework supplies the following APIs to handle building or tearing down that list.

struct fpga_region

FPGA Region structure

Definition:

struct fpga_region {
    struct device dev;
    struct mutex mutex;
    struct list_head bridge_list;
    struct fpga_manager *mgr;
    struct fpga_image_info *info;
    struct fpga_compat_id *compat_id;
    struct module *ops_owner;
    void *priv;
    int (*get_bridges)(struct fpga_region *region);
};

Members

dev

FPGA Region device

mutex

enforces exclusive reference to region

bridge_list

list of FPGA bridges specified in region

mgr

FPGA manager

info

FPGA image info

compat_id

FPGA region id for compatibility check.

ops_owner

module containing the get_bridges function

priv

private data

get_bridges

optional function to get bridges to a list

struct fpga_region_info

collection of parameters an FPGA Region

Definition:

struct fpga_region_info {
    struct fpga_manager *mgr;
    struct fpga_compat_id *compat_id;
    void *priv;
    int (*get_bridges)(struct fpga_region *region);
};

Members

mgr

fpga region manager

compat_id

FPGA region id for compatibility check.

priv

fpga region private data

get_bridges

optional function to get bridges to a list

Description

fpga_region_info contains parameters for the register_full function. These are separated into an info structure because they some are optional others could be added to in the future. The info structure facilitates maintaining a stable API.

struct fpga_region *__fpga_region_register_full(struct device *parent, const struct fpga_region_info *info, struct module *owner)

create and register an FPGA Region device

Parameters

struct device *parent

device parent

const struct fpga_region_info *info

parameters for FPGA Region

struct module *owner

module containing the get_bridges function

Return

struct fpga_region or ERR_PTR()

struct fpga_region *__fpga_region_register(struct device *parent, struct fpga_manager *mgr, int (*get_bridges)(struct fpga_region*), struct module *owner)

create and register an FPGA Region device

Parameters

struct device *parent

device parent

struct fpga_manager *mgr

manager that programs this region

int (*get_bridges)(struct fpga_region *)

optional function to get bridges to a list

struct module *owner

module containing the get_bridges function

Description

This simple version of the register function should be sufficient for most users. The fpga_region_register_full() function is available for users that need to pass additional, optional parameters.

Return

struct fpga_region or ERR_PTR()

void fpga_region_unregister(struct fpga_region *region)

unregister an FPGA region

Parameters

struct fpga_region *region

FPGA region

Description

This function is intended for use in an FPGA region driver’s remove function.

struct fpga_manager *fpga_mgr_get(struct device *dev)

Given a device, get a reference to an fpga mgr.

Parameters

struct device *dev

parent device that fpga mgr was registered with

Return

fpga manager struct or IS_ERR() condition containing error code.

struct fpga_manager *of_fpga_mgr_get(struct device_node *node)

Given a device node, get a reference to an fpga mgr.

Parameters

struct device_node *node

device node

Return

fpga manager struct or IS_ERR() condition containing error code.

void fpga_mgr_put(struct fpga_manager *mgr)

release a reference to an fpga manager

Parameters

struct fpga_manager *mgr

fpga manager structure

int fpga_bridge_get_to_list(struct device *dev, struct fpga_image_info *info, struct list_head *bridge_list)

given device, get a bridge, add it to a list

Parameters

struct device *dev

FPGA bridge device

struct fpga_image_info *info

fpga image specific information

struct list_head *bridge_list

list of FPGA bridges

Description

Get an exclusive reference to the bridge and it to the list.

Return

0 for success, error code from fpga_bridge_get() otherwise.

int of_fpga_bridge_get_to_list(struct device_node *np, struct fpga_image_info *info, struct list_head *bridge_list)

get a bridge, add it to a list

Parameters

struct device_node *np

node pointer of an FPGA bridge

struct fpga_image_info *info

fpga image specific information

struct list_head *bridge_list

list of FPGA bridges

Description

Get an exclusive reference to the bridge and it to the list.

Return

0 for success, error code from of_fpga_bridge_get() otherwise.

void fpga_bridges_put(struct list_head *bridge_list)

put bridges

Parameters

struct list_head *bridge_list

list of FPGA bridges

Description

For each bridge in the list, put the bridge and remove it from the list. If list is empty, do nothing.