linux-kernel - Re: FPGA programming driver architecture

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Message-Id: <200812131358.03010.florian@openwrt.org>
Date:	Sat, 13 Dec 2008 13:58:01 +0100
From:	Florian Fainelli <florian@...nwrt.org>
To:	Hugo Villeneuve <hugo@...ovil.com>
Cc:	linux-kernel@...r.kernel.org, linux-embedded@...r.kernel.org
Subject: Re: FPGA programming driver architecture

(CC'ing linux-embedded)

Salut Hugo,

Le Friday 12 December 2008 21:03:14 Hugo Villeneuve, vous avez écrit :
> 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.

Is it a platform-driver ? What do you provide in platform_data ?

>
> 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. 

You should probably consider using request_firmware to load the bitstream from 
the userspace and possibly add a /sys interface to export some attributes 
like :

- GPIOs being used between the host and the FPGA
- status (i.e : programmed, not programmed ...)
- FPGA vendor, type ...

> 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).

> 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.

What about something like that :

- fpgaload-core which contains all the code that can be shared between the 
drivers like requesting firmware, providing sysfs attributes, 
- fpgaload-spi would handle the low-level SPI connection
- fpgaload-par would handle the low-level parallel connection

fpgaload-ser and par would register with fpgaload-core and they could register 
a fpga loading callback which is low-level specific for instance. Platform 
code would instantiate the core driver. That way, adding support for other 
loading protocols like slave serial or master serial can be done easily.

>
> 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?
-- 
Best regards, Florian Fainelli
Email : florian@...nwrt.org
http://openwrt.org
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