Hi, Shawn,

On Tue, Feb 22, 2011 at 5:01 PM, Shawn Guo <email address hidden> wrote:
> I'm not sure when and how the issue was fixed, but it's gone on linux-
> linaro-2.6.38.  Either CONFIG_FIXED_PHY is selected or not, we do not
> have this issue, and fec driver works on mx51 babbage board.

Apparently, this commit fix this issue if you look at the git commit log:
and I have verified and result is that this commit did it in fact.

commit 6fcc040f02d281c7e9563127358a77ce2bbfe284
Author: Greg Ungerer <email address hidden>
Date:   Mon Oct 11 21:03:05 2010 +0000

    net: allow FEC driver to use fixed PHY support

    At least one board using the FEC driver does not have a conventional
    PHY attached to it, it is directly connected to a somewhat simple
    ethernet switch (the board is the SnapGear/LITE, and the attached
    4-port ethernet switch is a RealTek RTL8305). This switch does not
    present the usual register interface of a PHY, it presents nothing.
    So a PHY scan will find nothing - it finds ID's of 0 for each PHY
    on the attached MII bus.

    After the FEC driver was changed to use phylib for supporting PHYs
    it no longer works on this particular board/switch setup.

    Add code support to use a fixed phy if no PHY is found on the MII bus.
    This is based on the way the cpmac.c driver solved this same problem.

    Signed-off-by: Greg Ungerer <email address hidden>
    Signed-off-by: David S. Miller <email address hidden>



>
> ** Changed in: linux-linaro
>     Assignee: (unassigned) => Shawn Guo (shawn-gsc)
>
> ** Changed in: linux-linaro
>    Milestone: None => 11.05-final
>
> ** Changed in: linux-linaro
>   Importance: Undecided => Low
>
> ** Changed in: linux-linaro
>       Status: New => Invalid
>
> --
> You received this bug notification because you are a member of Linaro
> Kernel Working Group, which is the registrant for Linaro Linux.
> https://bugs.launchpad.net/bugs/655641
>
> Title:
>  mii_bus fails to register on imx51
>
> Status in Linaro Linux:
>  Invalid
>
> Bug description:
>  The mii_bus fails to register on imx51 and gives the following trace info.  Clean of CONFIG_FIXED_PHY can remove the error.
>
>  Fixed MDIO Bus: probed
>  FEC Ethernet Driver
>  ------------[ cut here ]------------
>  WARNING: at /build/buildd/linux-linaro-2.6.35/fs/sysfs/dir.c:451 sysfs_add_one+0
>  x6c/0x8c()
>  sysfs: cannot create duplicate filename '/class/mdio_bus/0'
>  Modules linked in:
>  Backtrace:
>  [<c0034540>] (dump_backtrace+0x0/0xf8) from [<c0308c68>] (dump_stack+0x18/0x1c)
>   r6:c03c0cef r5:000001c3 r4:df837d18 r3:f357b213
>  [<c0308c50>] (dump_stack+0x0/0x1c) from [<c0043d84>] (warn_slowpath_common+0x54/
>  0x6c)
>  [<c0043d30>] (warn_slowpath_common+0x0/0x6c) from [<c0043e40>] (warn_slowpath_fm
>  t+0x38/0x40)
>   r8:00000001 r7:df837d68 r6:df3dd090 r5:df811000 r4:ffffffef
>  r3:00000009
>  [<c0043e08>] (warn_slowpath_fmt+0x0/0x40) from [<c00ef150>] (sysfs_add_one+0x6c/
>  0x8c)
>   r3:df811000 r2:c03c0d20
>  [<c00ef0e4>] (sysfs_add_one+0x0/0x8c) from [<c00f00d0>] (sysfs_do_create_link+0x
>  fc/0x1cc)
>   r7:df85aa20 r6:df3dd000 r5:df3d1648 r4:df3dd090
>  [<c00effd4>] (sysfs_do_create_link+0x0/0x1cc) from [<c00f01cc>] (sysfs_create_li
>  nk+0x14/0x18)
>  [<c00f01b8>] (sysfs_create_link+0x0/0x18) from [<c0206b6c>] (device_add_class_sy
>  mlinks+0x5c/0xd8)
>  [<c0206b10>] (device_add_class_symlinks+0x0/0xd8) from [<c02072c0>] (device_add+
>  0x110/0x2dc)
>   r6:c041bda8 r5:00000000 r4:df3d1640 r3:00000000
>  [<c02071b0>] (device_add+0x0/0x2dc) from [<c02074a8>] (device_register+0x1c/0x20
>  )
>   r7:df3d1604 r6:df3d1640 r5:df3fc340 r4:df3d1640
>  [<c020748c>] (device_register+0x0/0x20) from [<c0238d00>] (mdiobus_register+0x90
>  /0x178)
>   r4:df3d1600 r3:00000000
>  [<c0238c70>] (mdiobus_register+0x0/0x178) from [<c023c51c>] (fec_enet_mii_init+0
>  x120/0x164)
>   r8:c041bda0 r7:00000080 r6:df3d1600 r5:df3fc340 r4:df3fc000
>  r3:df3d3ba0
>  [<c023c3fc>] (fec_enet_mii_init+0x0/0x164) from [<c0308494>] (fec_probe+0x170/0x
>  1f4)
>   r8:c041bda8 r7:df3fc340 r6:00000001 r5:c041bda0 r4:df3fc000
>  r3:ffc000f8
>  [<c0308324>] (fec_probe+0x0/0x1f4) from [<c020a840>] (platform_drv_probe+0x1c/0x
>  20)
>  [<c020a824>] (platform_drv_probe+0x0/0x20) from [<c0209754>] (really_probe+0xa0/
>  0x150)
>  [<c02096b4>] (really_probe+0x0/0x150) from [<c0209854>] (driver_probe_device+0x5
>  0/0x68)
>   r7:00000000 r6:c043e5f4 r5:c043e5f4 r4:c041bda8
>  [<c0209804>] (driver_probe_device+0x0/0x68) from [<c02098d4>] (__driver_attach+0
>  x68/0x8c)
>   r5:c041bddc r4:c041bda8
>  [<c020986c>] (__driver_attach+0x0/0x8c) from [<c0208ef8>] (bus_for_each_dev+0x54
>  /0x84)
>   r6:00000000 r5:c020986c r4:c043e5f4 r3:00000000
>  [<c0208ea4>] (bus_for_each_dev+0x0/0x84) from [<c02095c8>] (driver_attach+0x20/0
>  x28)
>   r6:c04369f8 r5:df3d3ae0 r4:c043e5f4
>  [<c02095a8>] (driver_attach+0x0/0x28) from [<c0208814>] (bus_add_driver+0xa4/0x1
>  9c)
>  [<c0208770>] (bus_add_driver+0x0/0x19c) from [<c0209c9c>] (driver_register+0xb0/
>  0xe4)
>   r7:00000013 r6:00000000 r5:c00086ec r4:c043e5f4
>  [<c0209bec>] (driver_register+0x0/0xe4) from [<c020ad44>] (platform_driver_regis
>  ter+0x4c/0x60)
>   r5:c00086ec r4:c001fa4c
>  [<c020acf8>] (platform_driver_register+0x0/0x60) from [<c001fa68>] (fec_enet_mod
>  ule_init+0x1c/0x28)
>  [<c001fa4c>] (fec_enet_module_init+0x0/0x28) from [<c002b340>] (do_one_initcall+
>  0x60/0x1c4)
>  [<c002b2e0>] (do_one_initcall+0x0/0x1c4) from [<c00086a4>] (do_initcalls+0x1c/0x
>  38)
>   r9:00000000 r8:00000000 r7:00000013 r6:c0047324 r5:c00086ec
>  r4:c0026840
>  [<c0008688>] (do_initcalls+0x0/0x38) from [<c00086e8>] (do_basic_setup+0x28/0x2c
>  )
>   r4:00000000 r3:00000000
>  [<c00086c0>] (do_basic_setup+0x0/0x2c) from [<c0008738>] (kernel_init+0x4c/0xec)
>  [<c00086ec>] (kernel_init+0x0/0xec) from [<c0047324>] (do_exit+0x0/0x258)
>   r4:00000000 r3:00000000
>  ---[ end trace 1c431abc57d885c7 ]---
>  mii_bus 0 failed to register
>