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 program an FPGA using a region

First, allocate the info struct:

info = fpga_image_info_alloc(dev);
if (!info)
        return -ENOMEM;

Set flags as needed, i.e.:

info->flags |= FPGA_MGR_PARTIAL_RECONFIG;

Point to your FPGA image, such as:

info->sgt = &sgt;

Add info to region and do the programming:

region->info = info;
ret = fpga_region_program_fpga(region);

fpga_region_program_fpga() operates on info passed in the fpga_image_info (region->info). This function will attempt to:

• lock the region’s mutex
• lock the region’s FPGA manager
• build a list of FPGA bridges if a method has been specified to do so
• disable the bridges
• program the FPGA
• re-enable the bridges
• release the locks

Then you will want to enumerate whatever hardware has appeared in the FPGA.

How to add a new FPGA region

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

[1]	(1, 2) ../devicetree/bindings/fpga/fpga-region.txt

[2]	../../drivers/fpga/of-fpga-region.c

API to program an FPGA

int fpga_region_program_fpga(struct fpga_region * region)

program FPGA

Parameters

struct fpga_region * region

FPGA region

Description

Program an FPGA using fpga image info (region->info). If the region has a get_bridges function, the exclusive reference for the bridges will be held if programming succeeds. This is intended to prevent reprogramming the region until the caller considers it safe to do so. The caller will need to call fpga_bridges_put() before attempting to reprogram the region.

Return 0 for success or negative error code.

API to add a new FPGA region

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;
  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.

priv

private data

get_bridges

optional function to get bridges to a list

struct fpga_region * fpga_region_create(struct device * dev, struct fpga_manager * mgr, int (*get_bridges) (struct fpga_region *)

alloc and init a struct fpga_region

Parameters

struct device * dev

device parent

struct fpga_manager * mgr

manager that programs this region

int (*)(struct fpga_region *) get_bridges

optional function to get bridges to a list

Return

struct fpga_region or NULL

void fpga_region_free(struct fpga_region * region)

free a struct fpga_region

Parameters

struct fpga_region * region

FPGA region created by fpga_region_create

int fpga_region_register(struct fpga_region * region)

register a FPGA region

Parameters

struct fpga_region * region

FPGA region created by fpga_region_create

Return

0 or -errno

void fpga_region_unregister(struct fpga_region * region)

unregister and free a FPGA region

Parameters

struct fpga_region * region

FPGA region