Hi,
I made some experiments using smsc91xx.
Now I have some problems with mdiobus_register.
This is the output:

smsc911x: Driver version 2008-10-21.
eth%d: smsc911x_init: Driver Parameters:
eth%d: smsc911x_init: LAN base: 0xD087A000
eth%d: smsc911x_init: IRQ: 317
eth%d: smsc911x_init: PHY will be autodetected.
eth%d: smsc911x_init: BYTE_TEST: 0x87654321
eth%d: smsc911x_init: LAN911x identified, idrev: 0x93110001, generation: 3
irq 317: nobody cared (try booting with the "irqpoll" option)
[<c0037518>] (unwind_backtrace+0x0/0xdc) from [<c007f61c>] (__report_bad_irq+0x30/0x88)
[<c007f61c>] (__report_bad_irq+0x30/0x88) from [<c007f7c0>] (note_interrupt+0x14c/0x1d0)
[<c007f7c0>] (note_interrupt+0x14c/0x1d0) from [<c0080068>] (handle_level_irq+0xa8/0xec)
[<c0080068>] (handle_level_irq+0xa8/0xec) from [<c00459c8>] (gpio_irq_handler+0xfc/0x12c)
[<c00459c8>] (gpio_irq_handler+0xfc/0x12c) from [<c003106c>] (asm_do_IRQ+0x6c/0x8c)
[<c003106c>] (asm_do_IRQ+0x6c/0x8c) from [<c0031a70>] (__irq_svc+0x30/0x80)
Exception stack(0xcfa67de8 to 0xcfa67e30)
7de0: 00000000 20000000 00000000 00000000 c044b430 cc832b00
7e00: 00000000 0000013d 60000013 cf9d1000 c044b450 cf9d1000 fb056000 cfa67e30
7e20: c007fa54 c007ef40 60000013 ffffffff
[<c0031a70>] (__irq_svc+0x30/0x80) from [<c007ef40>] (__setup_irq+0x22c/0x2f0)
[<c007ef40>] (__setup_irq+0x22c/0x2f0) from [<c007f0cc>] (request_threaded_irq+0xc8/0x110)
[<c007f0cc>] (request_threaded_irq+0xc8/0x110) from [<bf02a6fc>] (smsc911x_drv_probe+0x738/0x16ac [smsc911x])
[<bf02a6fc>] (smsc911x_drv_probe+0x738/0x16ac [smsc911x]) from [<c01c5a24>] (platform_drv_probe+0x18/0x1c)
[<c01c5a24>] (platform_drv_probe+0x18/0x1c) from [<c01c4bb4>] (driver_probe_device+0xa0/0x14c)
[<c01c4bb4>] (driver_probe_device+0xa0/0x14c) from [<c01c4cc0>] (__driver_attach+0x60/0x84)
[<c01c4cc0>] (__driver_attach+0x60/0x84) from [<c01c4488>] (bus_for_each_dev+0x44/0x74)
[<c01c4488>] (bus_for_each_dev+0x44/0x74) from [<c01c3da0>] (bus_add_driver+0x9c/0x220)
[<c01c3da0>] (bus_add_driver+0x9c/0x220) from [<c01c4f90>] (driver_register+0xa8/0x130)
[<c01c4f90>] (driver_register+0xa8/0x130) from [<c0031334>] (do_one_initcall+0x5c/0x1b4)
[<c0031334>] (do_one_initcall+0x5c/0x1b4) from [<c007bbdc>] (sys_init_module+0xb0/0x1dc)
[<c007bbdc>] (sys_init_module+0xb0/0x1dc) from [<c0031ec0>] (ret_fast_syscall+0x0/0x2c)
handlers:
[<bf029a68>] (smsc911x_irqhandler+0x0/0x4e4 [smsc911x])
Disabling IRQ #317
eth1: smsc911x_drv_probe: Network interface: "eth1"
eth1: smsc911x_mii_init: External PHY is not supported, using internal PHY
------------[ cut here ]------------
WARNING: at fs/sysfs/dir.c:477 sysfs_add_one+0x68/0x88()
sysfs: cannot create duplicate filename '/class/mdio_bus/ffffffff'
Modules linked in: smsc911x(+) [last unloaded: smsc911x]
[<c0037518>] (unwind_backtrace+0x0/0xdc) from [<c005808c>] (warn_slowpath_common+0x48/0x60)
[<c005808c>] (warn_slowpath_common+0x48/0x60) from [<c00580dc>] (warn_slowpath_fmt+0x24/0x30)
[<c00580dc>] (warn_slowpath_fmt+0x24/0x30) from [<c00ec1b0>] (sysfs_add_one+0x68/0x88)
[<c00ec1b0>] (sysfs_add_one+0x68/0x88) from [<c00ec700>] (create_dir+0x4c/0x90)
[<c00ec700>] (create_dir+0x4c/0x90) from [<c00ec77c>] (sysfs_create_dir+0x38/0x4c)
[<c00ec77c>] (sysfs_create_dir+0x38/0x4c) from [<c0179b58>] (kobject_add_internal+0xb8/0x18c)
[<c0179b58>] (kobject_add_internal+0xb8/0x18c) from [<c0179da0>] (kobject_add+0x48/0x58)
[<c0179da0>] (kobject_add+0x48/0x58) from [<c01c2948>] (device_add+0x94/0x534)
[<c01c2948>] (device_add+0x94/0x534) from [<c01e7328>] (mdiobus_register+0x88/0x170)
[<c01e7328>] (mdiobus_register+0x88/0x170) from [<bf02a948>] (smsc911x_drv_probe+0x984/0x16ac [smsc911x])
[<bf02a948>] (smsc911x_drv_probe+0x984/0x16ac [smsc911x]) from [<c01c5a24>] (platform_drv_probe+0x18/0x1c)
[<c01c5a24>] (platform_drv_probe+0x18/0x1c) from [<c01c4bb4>] (driver_probe_device+0xa0/0x14c)
[<c01c4bb4>] (driver_probe_device+0xa0/0x14c) from [<c01c4cc0>] (__driver_attach+0x60/0x84)
[<c01c4cc0>] (__driver_attach+0x60/0x84) from [<c01c4488>] (bus_for_each_dev+0x44/0x74)
[<c01c4488>] (bus_for_each_dev+0x44/0x74) from [<c01c3da0>] (bus_add_driver+0x9c/0x220)
[<c01c3da0>] (bus_add_driver+0x9c/0x220) from [<c01c4f90>] (driver_register+0xa8/0x130)
[<c01c4f90>] (driver_register+0xa8/0x130) from [<c0031334>] (do_one_initcall+0x5c/0x1b4)
[<c0031334>] (do_one_initcall+0x5c/0x1b4) from [<c007bbdc>] (sys_init_module+0xb0/0x1dc)
[<c007bbdc>] (sys_init_module+0xb0/0x1dc) from [<c0031ec0>] (ret_fast_syscall+0x0/0x2c)
---[ end trace c01592fb0d9f18f2 ]---
kobject_add_internal failed for ffffffff with -EEXIST, don't try to register things with the same name in the same directory.
[<c0037518>] (unwind_backtrace+0x0/0xdc) from [<c0179be4>] (kobject_add_internal+0x144/0x18c)
[<c0179be4>] (kobject_add_internal+0x144/0x18c) from [<c0179da0>] (kobject_add+0x48/0x58)
[<c0179da0>] (kobject_add+0x48/0x58) from [<c01c2948>] (device_add+0x94/0x534)
[<c01c2948>] (device_add+0x94/0x534) from [<c01e7328>] (mdiobus_register+0x88/0x170)
[<c01e7328>] (mdiobus_register+0x88/0x170) from [<bf02a948>] (smsc911x_drv_probe+0x984/0x16ac [smsc911x])
[<bf02a948>] (smsc911x_drv_probe+0x984/0x16ac [smsc911x]) from [<c01c5a24>] (platform_drv_probe+0x18/0x1c)
[<c01c5a24>] (platform_drv_probe+0x18/0x1c) from [<c01c4bb4>] (driver_probe_device+0xa0/0x14c)
[<c01c4bb4>] (driver_probe_device+0xa0/0x14c) from [<c01c4cc0>] (__driver_attach+0x60/0x84)
[<c01c4cc0>] (__driver_attach+0x60/0x84) from [<c01c4488>] (bus_for_each_dev+0x44/0x74)
[<c01c4488>] (bus_for_each_dev+0x44/0x74) from [<c01c3da0>] (bus_add_driver+0x9c/0x220)
[<c01c3da0>] (bus_add_driver+0x9c/0x220) from [<c01c4f90>] (driver_register+0xa8/0x130)
[<c01c4f90>] (driver_register+0xa8/0x130) from [<c0031334>] (do_one_initcall+0x5c/0x1b4)
[<c0031334>] (do_one_initcall+0x5c/0x1b4) from [<c007bbdc>] (sys_init_module+0xb0/0x1dc)
[<c007bbdc>] (sys_init_module+0xb0/0x1dc) from [<c0031ec0>] (ret_fast_syscall+0x0/0x2c)
mii_bus ffffffff failed to register
eth1: smsc911x_mii_init: Error registering mii bus
eth1: smsc911x_drv_probe: Error -6 initialising mii


Have you some advice?
Best Regards,
Alberto