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This patch contains UDM-design.txt, which is document containing general description of the driver model. The remaining files contains descriptions of conversion process of particular subsystems. Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
116 lines
4.0 KiB
Plaintext
116 lines
4.0 KiB
Plaintext
The U-Boot Driver Model Project
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===============================
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I/O system analysis
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===================
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Marek Vasut <marek.vasut@gmail.com>
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2012-02-21
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I) Overview
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-----------
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The current FPGA implementation is handled by command "fpga". This command in
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turn calls the following functions:
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fpga_info()
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fpga_load()
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fpga_dump()
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These functions are implemented by what appears to be FPGA multiplexer, located
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in drivers/fpga/fpga.c . This code determines which device to operate with
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depending on the device ID.
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The fpga_info() function is multiplexer of the functions providing information
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about the particular FPGA device. These functions are implemented in the drivers
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for the particular FPGA device:
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xilinx_info()
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altera_info()
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lattice_info()
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Similar approach is used for fpga_load(), which multiplexes "xilinx_load()",
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"altera_load()" and "lattice_load()" and is used to load firmware into the FPGA
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device.
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The fpga_dump() function, which prints the contents of the FPGA device, is no
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different either, by multiplexing "xilinx_dump()", "altera_dump()" and
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"lattice_dump()" functions.
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Finally, each new FPGA device is registered by calling "fpga_add()" function.
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This function takes two arguments, the second one being particularly important,
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because it's basically what will become platform_data. Currently, it's data that
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are passed to the driver from the board/platform code.
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II) Approach
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------------
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The path to conversion of the FPGA subsystem will be very straightforward, since
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the FPGA subsystem is already quite dynamic. Multiple things will need to be
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modified though.
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First is the registration of the new FPGA device towards the FPGA core. This
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will be achieved by calling:
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fpga_device_register(struct instance *i, const struct fpga_ops *ops);
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The particularly interesting part is the struct fpga_ops, which contains
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operations supported by the FPGA device. These are basically the already used
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calls in the current implementation:
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struct fpga_ops {
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int info(struct instance *i);
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int load(struct instance *i, const char *buf, size_t size);
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int dump(struct instance *i, const char *buf, size_t size);
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}
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The other piece that'll have to be modified is how the devices are tracked.
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It'll be necessary to introduce a linked list of devices within the FPGA core
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instead of tracking them by ID number.
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Next, the "Xilinx_desc", "Lattice_desc" and "Altera_desc" structures will have
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to be moved to driver's private_data. Finally, structures passed from the board
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and/or platform files, like "Xilinx_Virtex2_Slave_SelectMap_fns" would be passed
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via platform_data to the driver.
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III) Analysis of in-tree drivers
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--------------------------------
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1) Altera driver
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----------------
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The driver is realized using the following files:
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drivers/fpga/altera.c
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drivers/fpga/ACEX1K.c
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drivers/fpga/cyclon2.c
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drivers/fpga/stratixII.c
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All of the sub-drivers implement basically the same info-load-dump interface
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and there's no expected problem during the conversion. The driver itself will
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be realised by altera.c and all the sub-drivers will be linked in. The
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distinction will be done by passing different platform data.
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2) Lattice driver
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-----------------
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The driver is realized using the following files:
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drivers/fpga/lattice.c
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drivers/fpga/ivm_core.c
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This driver also implements the standard interface, but to realise the
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operations with the FPGA device, uses functions from "ivm_core.c" file. This
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file implements the main communications logic and has to be linked in together
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with "lattice.c". No problem converting is expected here.
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3) Xilinx driver
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----------------
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The driver is realized using the following files:
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drivers/fpga/xilinx.c
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drivers/fpga/spartan2.c
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drivers/fpga/spartan3.c
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drivers/fpga/virtex2.c
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This set of sub-drivers is special by defining a big set of macros in
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"include/spartan3.h" and similar files. These macros would need to be either
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rewritten or replaced. Otherwise, there are no problems expected during the
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conversion process.
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