FPGA Manager¶

Overview¶

The FPGA manager core exports a set of functions for programming an FPGA with an image. The API is manufacturer agnostic. All manufacturer specifics are hidden away in a low level driver which registers a set of ops with the core. The FPGA image data itself is very manufacturer specific, but for our purposes it’s just binary data. The FPGA manager core won’t parse it.

The FPGA image to be programmed can be in a scatter gather list, a single contiguous buffer, or a firmware file. Because allocating contiguous kernel memory for the buffer should be avoided, users are encouraged to use a scatter gather list instead if possible.

The particulars for programming the image are presented in a structure (struct fpga_image_info). This struct contains parameters such as pointers to the FPGA image as well as image-specific particulars such as whether the image was built for full or partial reconfiguration.

How to support a new FPGA device¶

To add another FPGA manager, write a driver that implements a set of ops. The probe function calls fpga_mgr_register(), such as:

static const struct fpga_manager_ops socfpga_fpga_ops = {
        .write_init = socfpga_fpga_ops_configure_init,
        .write = socfpga_fpga_ops_configure_write,
        .write_complete = socfpga_fpga_ops_configure_complete,
        .state = socfpga_fpga_ops_state,
};

static int socfpga_fpga_probe(struct platform_device *pdev)
{
        struct device *dev = &pdev->dev;
        struct socfpga_fpga_priv *priv;
        struct fpga_manager *mgr;
        int ret;

        priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        /*
         * do ioremaps, get interrupts, etc. and save
         * them in priv
         */

        mgr = devm_fpga_mgr_create(dev, "Altera SOCFPGA FPGA Manager",
                                   &socfpga_fpga_ops, priv);
        if (!mgr)
                return -ENOMEM;

        platform_set_drvdata(pdev, mgr);

        return fpga_mgr_register(mgr);
}

static int socfpga_fpga_remove(struct platform_device *pdev)
{
        struct fpga_manager *mgr = platform_get_drvdata(pdev);

        fpga_mgr_unregister(mgr);

        return 0;
}

The ops will implement whatever device specific register writes are needed to do the programming sequence for this particular FPGA. These ops return 0 for success or negative error codes otherwise.

The programming sequence is::

.write_init
.write or .write_sg (may be called once or multiple times)
.write_complete

The .write_init function will prepare the FPGA to receive the image data. The buffer passed into .write_init will be at most .initial_header_size bytes long; if the whole bitstream is not immediately available then the core code will buffer up at least this much before starting.

The .write function writes a buffer to the FPGA. The buffer may be contain the whole FPGA image or may be a smaller chunk of an FPGA image. In the latter case, this function is called multiple times for successive chunks. This interface is suitable for drivers which use PIO.

The .write_sg version behaves the same as .write except the input is a sg_table scatter list. This interface is suitable for drivers which use DMA.

The .write_complete function is called after all the image has been written to put the FPGA into operating mode.

The ops include a .state function which will determine the state the FPGA is in and return a code of type enum fpga_mgr_states. It doesn’t result in a change in state.

API for implementing a new FPGA Manager driver¶

fpga_mgr_states — Values for fpga_manager->state.
struct fpga_manager — the FPGA manager struct
struct fpga_manager_ops — Low level FPGA manager driver ops
devm_fpga_mgr_create() — Allocate and init a manager struct
fpga_mgr_register() — Register an FPGA manager
fpga_mgr_unregister() — Unregister an FPGA manager

enum fpga_mgr_states¶: fpga framework states

Constants

FPGA_MGR_STATE_UNKNOWN: can’t determine state
FPGA_MGR_STATE_POWER_OFF: FPGA power is off
FPGA_MGR_STATE_POWER_UP: FPGA reports power is up
FPGA_MGR_STATE_RESET: FPGA in reset state
FPGA_MGR_STATE_FIRMWARE_REQ: firmware request in progress
FPGA_MGR_STATE_FIRMWARE_REQ_ERR: firmware request failed
FPGA_MGR_STATE_WRITE_INIT: preparing FPGA for programming
FPGA_MGR_STATE_WRITE_INIT_ERR: Error during WRITE_INIT stage
FPGA_MGR_STATE_WRITE: writing image to FPGA
FPGA_MGR_STATE_WRITE_ERR: Error while writing FPGA
FPGA_MGR_STATE_WRITE_COMPLETE: Doing post programming steps
FPGA_MGR_STATE_WRITE_COMPLETE_ERR: Error during WRITE_COMPLETE
FPGA_MGR_STATE_OPERATING: FPGA is programmed and operating

struct fpga_manager¶: fpga manager structure

Definition

struct fpga_manager {
  const char *name;
  struct device dev;
  struct mutex ref_mutex;
  enum fpga_mgr_states state;
  struct fpga_compat_id *compat_id;
  const struct fpga_manager_ops *mops;
  void *priv;
};

Members

name: name of low level fpga manager
dev: fpga manager device
ref_mutex: only allows one reference to fpga manager
state: state of fpga manager
compat_id: FPGA manager id for compatibility check.
mops: pointer to struct of fpga manager ops
priv: low level driver private date

struct fpga_manager_ops¶: ops for low level fpga manager drivers

Definition

struct fpga_manager_ops {
  size_t initial_header_size;
  enum fpga_mgr_states (*state)(struct fpga_manager *mgr);
  u64 (*status)(struct fpga_manager *mgr);
  int (*write_init)(struct fpga_manager *mgr,struct fpga_image_info *info, const char *buf, size_t count);
  int (*write)(struct fpga_manager *mgr, const char *buf, size_t count);
  int (*write_sg)(struct fpga_manager *mgr, struct sg_table *sgt);
  int (*write_complete)(struct fpga_manager *mgr, struct fpga_image_info *info);
  void (*fpga_remove)(struct fpga_manager *mgr);
  const struct attribute_group **groups;
};

Members

initial_header_size: Maximum number of bytes that should be passed into write_init
state: returns an enum value of the FPGA’s state
status: returns status of the FPGA, including reconfiguration error code
write_init: prepare the FPGA to receive confuration data
write: write count bytes of configuration data to the FPGA
write_sg: write the scatter list of configuration data to the FPGA
write_complete: set FPGA to operating state after writing is done
fpga_remove: optional: Set FPGA into a specific state during driver remove
groups: optional attribute groups.

Description

fpga_manager_ops are the low level functions implemented by a specific fpga manager driver. The optional ones are tested for NULL before being called, so leaving them out is fine.

struct fpga_manager * devm_fpga_mgr_create(struct device *dev, const char *name, const struct fpga_manager_ops *mops, void *priv)¶: create and initialize a managed FPGA manager struct

Parameters

struct device *dev: fpga manager device from pdev
const char *name: fpga manager name
const struct fpga_manager_ops *mops: pointer to structure of fpga manager ops
void *priv: fpga manager private data

Description

This function is intended for use in a FPGA manager driver’s probe function. After the manager driver creates the manager struct with devm_fpga_mgr_create(), it should register it with fpga_mgr_register(). The manager driver’s remove function should call fpga_mgr_unregister(). The manager struct allocated with this function will be freed automatically on driver detach. This includes the case of a probe function returning error before calling fpga_mgr_register(), the struct will still get cleaned up.

Return

pointer to struct fpga_manager or NULL

int fpga_mgr_register(struct fpga_manager *mgr)¶: register a FPGA manager

Parameters

struct fpga_manager *mgr: fpga manager struct

Return

0 on success, negative error code otherwise.

void fpga_mgr_unregister(struct fpga_manager *mgr)¶: unregister a FPGA manager

Parameters

struct fpga_manager *mgr: fpga manager struct

Description

This function is intended for use in a FPGA manager driver’s remove function.