Re: Multiple device attachments

[Michael <macallan%netbsd.org@localhost>]

Hello,

On Thu, 21 Jul 2011 14:44:04 -0500
Frank Zerangue <frank.zerangue%gmail.com@localhost> wrote:

> /sys/device.h -- seems to indicate that a device driver can attach to 
> multiple parent
> drivers (e.g. busses, controllers, ?)
> 
> /*
>  * Devices can have multiple configuration attachments if they attach
>  * to different attributes (busses, or whatever), to allow specification
>  * of multiple match and attach functions.  There is only one configuration
>  * driver per driver, so that things like unit numbers and the device
>  * structure array will be shared.
>  */
> 
> Does anyone know how this is done in practice?

You split the driver in bus-dependent and bus-independent portions - the former 
does stuff like match & attach, find and map registers etc., the latter is the 
actual driver. There are plenty examples in the source tree:
- hme, gem exist as pci and sbus variants
- le, esp, com have lots of different bus backends ( Try to find a 1990s UNIX 
workstation that has neither an le nor an esp. Suns used both as sbus devices, 
others used their own buses or had them embedded in custom IO chips. )
- chipsfb and igsfb supports both pci and ofbus ( actually vlb with 
OpenFirmware glue, see arch/shark/ofw/chipsfb_ofbus.c, igsfb_ofbus.c )

have fun
Michael
-- 
Michael <macallan%netbsd.org@localhost>