xref: /kernel/linux/linux-5.10/Documentation/driver-api/fpga/fpga-mgr.rst

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::
 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 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 :c:expr:`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

.. kernel-doc:: include/linux/fpga/fpga-mgr.h
   :functions: fpga_mgr_states

.. kernel-doc:: include/linux/fpga/fpga-mgr.h
   :functions: fpga_manager

.. kernel-doc:: include/linux/fpga/fpga-mgr.h
   :functions: fpga_manager_ops

.. kernel-doc:: drivers/fpga/fpga-mgr.c
   :functions: devm_fpga_mgr_create

.. kernel-doc:: drivers/fpga/fpga-mgr.c
   :functions: fpga_mgr_register

.. kernel-doc:: drivers/fpga/fpga-mgr.c
   :functions: fpga_mgr_unregister