linux-kernel - Re: driver model advice

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Message-ID: <10f740e80906072336n5e7b3d4te5834ff89b277bd0@mail.gmail.com>
Date:	Mon, 8 Jun 2009 08:36:36 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Alexander Clouter <alex@...riz.org.uk>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: driver model advice

On Mon, Jun 8, 2009 at 00:45, Alexander Clouter<alex@...riz.org.uk> wrote:
> For a while I have been maintaining the TS-7800 mainline support[1] and
> decided to attempt to properly address support for the FPGA on the
> board.
>
> Currently the solution I'm using[2] is not very flexible and scalable as
> for every device that is added the platform code grows with it.  I also
> think it's just not very pretty.
>
> I have been reading various sources of documentation regarding the
> driver model and relevant sections in the LDD tomb and felt that making
> the FPGA behave as a bus seemed a neat way to do things.
>
> A quick overview of the approach I'm using is that the bus code adds and
> removes the devices depending on the bus's state ('online' or
> 'offline').  When going online (or as new drivers are insmod'ed) the bus
> decides if the 'discover' function should be executed depending on the
> FPGA bitstream magic number and then if the driver's discover() function
> decides the device is present it is added to the bus.

You can make it a separate bus...

> The code for my amendments can be found (it's 30kB hence why it's not
> inline), it's been written against 2.6.30-rc7:
>
> http://stuff.digriz.org.uk/ts78xx-fpga/fpga-device-work.diff
>
> and the my .config file is:
>
> http://stuff.digriz.org.uk/ts78xx-fpga/ts78xx.config
>
> One thing that might make people 'queasy' is that there is some wrapper
> code for platform drivers.  Although all the examples I have coded up
> use platform drivers and create platform devices, there are some drivers
> that are non-platform based in the works (GPIO, AVR, ISA bus, etc).  I
> felt the appropriate approach was (bearing in mind that different FPGA
> bitstreams implement possibly overlapping/partial duplicate
> functionality) to use a platform wrapper, the platform device being a
> child of my ts78xx-fgpa device.

... or you can make the ts78xx-fpga device a multi-function device
(drivers/mfd).

(In case the mfd-ers read this: recently I've been looking at using the mfd code
 for Amiga Zorro expansion boards. As most Zorro boards are made from discrete
 components, several of them are actually multi-function devices,
which prohibits
 me from just using zorro_driver).

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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