Hi,
I have written some code to program a FPGA in Linux, for two different types of
boards: one uses a serial interface (SPI) and the second a parallel interface.
I have been able to sucessfully program both boards. I'm now trying to clean my
code and make it more generic, as well as better in line with the Linux driver
model. I would also like to include it in the mainline kernel if there is
interest.
Here is a description of the current architecture (refer to diagrams below):
The fpgaload module controls one output GPIOs (PROG), and two input GPIOs (INIT
and DONE). These GPIOs are specified in board setup code. Both fpgaload_ser and
fpgaload_par modules export a single function to write a byte. The fpgaload
driver is a char device to which we can write (/dev/fpgaload) to program a
bitstream (FPGA firmware) inside the FPGA. The fpgaload driver will toggle the
GPIOs to initiate programming and the then call the corresponding write_byte
function based on the interface type specified in board setup code (serial or
parallel, or any future interface desired).
FPGA serial bitstream loading architecture
+----------------------+
| FPGA load driver |
| (fpgaload) |
+----------------------+
| |
| +----------------+
| | FPGA serial |
| | load driver |
| | (fpgaload_ser) |
| +----------------+
| |
| +-------------------+
| | SPI master |
| | controller driver |
| +-------------------+
| |
| | Linux
------------------------------------
| | HARDWARE
| |spi
| |
| +--------------+
| | SPI |
+----->| Programming |
GPIOs | interface |
+--------------+
FPGA
FPGA parallel bitstream loading architecture
+----------------------+
| FPGA load driver |
| (fpgaload) |
+----------------------+
| |
| +----------------+
| | FPGA parallel |
| | load driver |
| | (fpgaload_par) |
| +----------------+
| |
| | Linux
------------------------------------
| | HARDWARE
| |parallel
| |
| +--------------+
| | Parallel |
+----->| Programming |
GPIOs | interface |
+--------------+
FPGA
The problem with that approach is that when loading the fpgaload module with
modprobe, it will automatically try to load the fpgaload_ser and fpgaload_par
modules, even if only serial interface was specified in board setup code for
example. This is not good when building a kernel for similar but different
boards.
Probably a better approach would be for the fpgaload_Ser and fpgaload_par
modules to register themselves with the fpgaload module. Then, should the
fpgaload module be built using a BUS driver structure? Or anyone having any
suggestions on how it should be implemented?
Hugo Villeneuve
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