Attaching pseudo bus to i386 nexus bus.

[ss griffon]

On Tue, Dec 20, 2011 at 8:55 PM, ss griffon <ssgriffonuser at gmail.com> wrote:
> I've been playing around with the hdac sound driver and as an exercise
> I decided to make my own "pseudo" pcm driver.  However, I can't seem
> to get my device_probe and device_attach functions to be called on my
> "pseudo" bus driver.  I've spent a lot of time looking at the bus code
> in kernel/subr_bus.c and I think I have a good understanding of it but
> apparently not good enough.  I've looked at other devices that
> implement buses, such as hdac, pci and acpi (which hangs off of nexus
> as well) and I can't find what they are doing to make their
> device_probe/device_attach to be called.  Perhaps my driver is missing
> a reference to a parent?  Anyway, any help would be greatly
> appreciated, maybe it is something very obvious.  I turned on the
> BUS_DEBUG option and provide it's output along with the code.
>
> Code:
>
> #ifdef HAVE_KERNEL_OPTION_HEADERS
> #include "opt_snd.h"
> #endif
>
> #include <dev/sound/pcm/sound.h>
> #include <dev/sound/pcm/pcm.h>
>
> #include "device_if.h"
> #include "bus_if.h"
> #include "mixer_if.h"
>
> static int
> snd_loop_bus_probe(device_t dev)
> {
>  printf("%s %d called\n", __func__, __LINE__);
>  return 0;
> }
>
> static int
> snd_loop_bus_attach(device_t dev)
> {
>  printf("%s %d called\n", __func__, __LINE__);
>  return 0;
> }
>
> static void
> snd_loop_bus_driver_added(device_t dev, driver_t *driver)
> {
>  printf("%s %d called\n", __func__, __LINE__);
> }
>
> static device_method_t snd_loop_bus_methods[] = {
>  DEVMETHOD(device_probe,       snd_loop_bus_probe),
>  DEVMETHOD(device_attach,      snd_loop_bus_attach),
>  /*Bus Interface*/
>  DEVMETHOD(bus_driver_added,   snd_loop_bus_driver_added),
>  { 0, 0 }
> };
>
> static driver_t snd_loop_bus_driver = {
>  "snd_loop_bus",
>  snd_loop_bus_methods,
>  PCM_SOFTC_SIZE, /*This isn't used, should be 1*/
> };
>
> devclass_t snd_loop_bus_devclass;
> DRIVER_MODULE(snd_loop_bus, nexus, snd_loop_bus_driver,
> snd_loop_bus_devclass, 0, 0);
>
>
>
> BUS_DEBUG Output:
>bus
> devclass_find_internal:914: looking for nexus
> driver_module_handler:4462: Loading module: driver snd_loop_bus on bus
> nexus (pass 2147483647)
> devclass_add_driver:1047: snd_loop_bus
> devclass_find_internal:914: looking for snd_loop_bus
> devclass_find_internal:924: creating snd_loop_bus

In case anyone is interested, I got this figured out.  If you want to
add a device to the nexus bus you must implement the device_identify
method.  From device identify, you can call BUS_ADD_CHILD and add your
driver to the nexus bus.  This seems to be necessary for the nexus bus
and some other buses that do not implement bus_driver_added which is
where buses can probe and attach the driver.  So if you add your
device to the "pci" bus, your device_probe and device_attach methods
will be called automatically.

sys/dev/nvram2env is a good simple example of adding a device to the nexus bus.