Re: Driver framework: binding a driver to two devices?

From: Geert Uytterhoeven
Date: Sun Aug 14 2011 - 15:33:26 EST

On Sun, Aug 14, 2011 at 19:38, Greg KH <greg@xxxxxxxxx> 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
>> Â Â dev1 = zorro_find_device(id1, ...)
>> Â Â 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? ÂThat 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. ÂUSB 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?



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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.
             Â Â -- Linus Torvalds
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