FPGA Manager Core

Alan Tull 2015

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.

API Functions:
==============

To program the FPGA:
--------------------

	int fpga_mgr_load(struct fpga_manager *mgr,
			  struct fpga_image_info *info);

Load the FPGA from an image which is indicated in the info.  If successful,
the FPGA ends up in operating mode.  Return 0 on success or a negative error
code.

To allocate or free a struct fpga_image_info:
---------------------------------------------

	struct fpga_image_info *fpga_image_info_alloc(struct device *dev);

	void fpga_image_info_free(struct fpga_image_info *info);

To get/put a reference to a FPGA manager:
-----------------------------------------

	struct fpga_manager *of_fpga_mgr_get(struct device_node *node);
	struct fpga_manager *fpga_mgr_get(struct device *dev);
	void fpga_mgr_put(struct fpga_manager *mgr);

Given a DT node or device, get a reference to a FPGA manager.  This pointer
can be saved until you are ready to program the FPGA.  fpga_mgr_put releases
the reference.


To get exclusive control of a FPGA manager:
-------------------------------------------

	int fpga_mgr_lock(struct fpga_manager *mgr);
	void fpga_mgr_unlock(struct fpga_manager *mgr);

The user should call fpga_mgr_lock and verify that it returns 0 before
attempting to program the FPGA.  Likewise, the user should call
fpga_mgr_unlock when done programming the FPGA.


To register or unregister the low level FPGA-specific driver:
-------------------------------------------------------------

	int fpga_mgr_register(struct device *dev, const char *name,
			      const struct fpga_manager_ops *mops,
			      void *priv);

	void fpga_mgr_unregister(struct device *dev);

Use of these two functions is described below in "How To Support a new FPGA
device."


How to write an image buffer to a supported FPGA
================================================
#include <linux/fpga/fpga-mgr.h>

struct fpga_manager *mgr;
struct fpga_image_info *info;
int ret;

/*
 * Get a reference to FPGA manager.  The manager is not locked, so you can
 * hold onto this reference without it preventing programming.
 *
 * This example uses the device node of the manager.  Alternatively, use
 * fpga_mgr_get(dev) instead if you have the device.
 */
mgr = of_fpga_mgr_get(mgr_node);

/* struct with information about the FPGA image to program. */
info = fpga_image_info_alloc(dev);

/* flags indicates whether to do full or partial reconfiguration */
info->flags = FPGA_MGR_PARTIAL_RECONFIG;

/*
 * At this point, indicate where the image is. This is pseudo-code; you're
 * going to use one of these three.
 */
if (image is in a scatter gather table) {

	info->sgt = [your scatter gather table]

} else if (image is in a buffer) {

	info->buf = [your image buffer]
	info->count = [image buffer size]

} else if (image is in a firmware file) {

	info->firmware_name = devm_kstrdup(dev, firmware_name, GFP_KERNEL);

}

/* Get exclusive control of FPGA manager */
ret = fpga_mgr_lock(mgr);

/* Load the buffer to the FPGA */
ret = fpga_mgr_buf_load(mgr, &info, buf, count);

/* Release the FPGA manager */
fpga_mgr_unlock(mgr);
fpga_mgr_put(mgr);

/* Deallocate the image info if you're done with it */
fpga_image_info_free(info);

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;
	int ret;

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

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

	return fpga_mgr_register(dev, "Altera SOCFPGA FPGA Manager",
				 &socfpga_fpga_ops, priv);
}

static int socfpga_fpga_remove(struct platform_device *pdev)
{
	fpga_mgr_unregister(&pdev->dev);

	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:
 1. .write_init
 2. .write or .write_sg (may be called once or multiple times)
 3. .write_complete

The .write_init function will prepare the FPGA to receive the image data.  The
buffer passed into .write_init will be atmost .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 read the hardware FPGA manager and
return a code of type enum fpga_mgr_states.  It doesn't result in a change in
hardware state.