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

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Message-ID: <CAMuHMdUdJvqm+U7EY-p+vmkKyBd7urcRYEfV_6BWU8zqo+b_tA@mail.gmail.com>
Date:	Sun, 14 Aug 2011 21:32:01 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org,
	"Linux/m68k" <linux-m68k@...r.kernel.org>
Subject: Re: Driver framework: binding a driver to two devices?

On Sun, Aug 14, 2011 at 19:38, Greg KH <greg@...ah.com> wrote:
> On Sat, Aug 13, 2011 at 10:44:42PM +0200, Geert Uytterhoeven wrote:
>> 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?
>
> What you really want is the same "driver instance" bound to two devices,
> right?  That way the device would operate "knowing" about both physical
> devices so as to properly control the thing.

Yes, that's what I want.

> Right now, no, there's not a simple way to do this with the driver
> model.  USB does this on its own for some devices that need to have
> multiple "interfaces" (the USB equalivant for a "device") controlled at
> the same time, so you might want to look at how that happens (in the
> indivdual drivers, not in the USB core.)

Thanks, I'll have a look at the USB drivers.
Do you know which examples to look at?

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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