linux-kernel - Driver framework: binding a driver to two devices?

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Date:	Sat, 13 Aug 2011 22:44:42 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	linux-kernel@...r.kernel.org
Cc:	"Linux/m68k" <linux-m68k@...r.kernel.org>
Subject: Driver framework: binding a driver to two devices?

As Amiga Zorro expansion boards have only one BAR (unlike PCI, which has
multiple BARs), several Amiga graphics cards show up as two Zorro devices:
one for the graphics memory and one for the graphics controller's registers.

Traditionally, a driver for such a device used

    dev1 = zorro_find_device(id1, ...)
    dev2 = zorro_find_device(id2, ...)

to find the two devices and match them.

With the "new" driver framework, the matching with device id1 is now
done using a
struct zorro_driver with a table of IDs, while the matching with device id2 is
still done by calling zorro_find_device(id2, ...).

Recently (with cirrusfb) it turned out that the call to
zorro_find_device(id2, ...)
may fail to find the second device. I suspect this happens due to the second
device haven't been probed for at the time the zorro_driver for the
first device is
initialized.

I expect this can be fixed by delaying all calls to device_register() in
amiga_zorro_probe() until all devices have been detected and added to the array
used by zorro_find_device(). But I was wondering whether there's a more generic
way in the driver framework to bind a driver to two devices?

Are there any PCI devices that show similar behavior?
I know some PCI drivers look up data in DMI tables, but that's not
really the same.

Thanks in advance!

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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