[PATCH] ARM: integrator: fix OF-related regression

On Thu, Jun 26, 2014 at 02:15:42PM +0200, Linus Walleij wrote:

On Wed, Jun 25, 2014 at 3:06 PM, Rob Herring [off-list ref] wrote:

quoted

On Tue, Jun 24, 2014 at 7:08 AM, Linus Walleij [off-list ref] wrote:

quoted

Commit 07e461cd7e73a84f0e3757932b93cc80976fd749
"of: Ensure unique names without sacrificing determinism"
caused a boot failure regression on the Integrator machines.

The problem is probably caused by fiddling too much with
the device tree population in the OF init function, such
as passing the SoC bus device as parent when populating
the device tree.

This patch fixes the problem by:

- Avoiding to explicitly look up the tree root
- Look up devices needed before device population from
  the match only, passing NULL as root
- Passing NULL as root and parent when calling
  of_platform_populate()

Just curious, I don't see how this fixes booting for Integrator. Where
exactly does boot fail?

It fails by failing to populate the devicetree somehow. I don't
have the proper debugging needs, I just trial-and-horror-fixed
it by making the board init similar to other platforms :-/

earlyprintk doesn't work on Integrator hardware?  It does on QEMU's
integratorcp so it's trivial to debug there.

The problem is that integrator_init_sysfs() adds a device attribute
called "fpga" to the soc0 bus, and the soc0 bus device is also used as
the root of the device tree, and the device tree has a node called "fpga".

Before 07e461cd7e73a84f0e3757932b93cc80976fd749 this node directory and
attribute file had unique paths:

	sysfs: creating file '/devices/soc0/fpga'
	sysfs: creating dir '/devices/soc0/fpga.0'

07e461cd7e73a84f0e3757932b93cc80976fd749 removed the .0 from the fpga node's
directory, leading to that node (and its subnodes) failing to register due to a
filename conflict with the fpga attribute's file:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at /home/rabin/dev/linux/fs/sysfs/dir.c:31 sysfs_warn_dup+0x54/0x74()
sysfs: cannot create duplicate filename '/devices/soc0/fpga'
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Not tainted 3.15.0-rc5-00030-g244fb0a #17
[<c000ea34>] (unwind_backtrace) from [<c000c18c>] (show_stack+0x10/0x14)
[<c000c18c>] (show_stack) from [<c00193f0>] (warn_slowpath_common+0x64/0x84)
[<c00193f0>] (warn_slowpath_common) from [<c0019440>] (warn_slowpath_fmt+0x30/0x40)
[<c0019440>] (warn_slowpath_fmt) from [<c0104008>] (sysfs_warn_dup+0x54/0x74)
[<c0104008>] (sysfs_warn_dup) from [<c01040b0>] (sysfs_create_dir_ns+0x88/0x98)
[<c01040b0>] (sysfs_create_dir_ns) from [<c0188410>] (kobject_add_internal+0xac/0x2fc)
[<c0188410>] (kobject_add_internal) from [<c0188820>] (kobject_add+0x4c/0x98)
[<c0188820>] (kobject_add) from [<c01edacc>] (device_add+0xe0/0x4f0)
[<c01edacc>] (device_add) from [<c02559b0>] (of_platform_device_create_pdata+0x6c/0x8c)
[<c02559b0>] (of_platform_device_create_pdata) from [<c0255aac>] (of_platform_bus_create+0xd0/0x2b4)
[<c0255aac>] (of_platform_bus_create) from [<c0255db8>] (of_platform_populate+0x5c/0xa0)
[<c0255db8>] (of_platform_populate) from [<c0415fdc>] (customize_machine+0x20/0x44)
[<c0415fdc>] (customize_machine) from [<c0008b6c>] (do_one_initcall+0xfc/0x160)
[<c0008b6c>] (do_one_initcall) from [<c0413b40>] (kernel_init_freeable+0xf4/0x1ac)
[<c0413b40>] (kernel_init_freeable) from [<c0312b60>] (kernel_init+0x8/0xec)
[<c0312b60>] (kernel_init) from [<c0009830>] (ret_from_fork+0x14/0x24)
---[ end trace b6f453d64d825b4b ]---
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at /home/rabin/dev/linux/lib/kobject.c:240 kobject_add_internal+0x274/0x2fc()
kobject_add_internal failed for fpga with -EEXIST, don't try to register things with the same name in the same directory.
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Tainted: G        W     3.15.0-rc5-00030-g244fb0a #17
[<c000ea34>] (unwind_backtrace) from [<c000c18c>] (show_stack+0x10/0x14)
[<c000c18c>] (show_stack) from [<c00193f0>] (warn_slowpath_common+0x64/0x84)
[<c00193f0>] (warn_slowpath_common) from [<c0019440>] (warn_slowpath_fmt+0x30/0x40)
[<c0019440>] (warn_slowpath_fmt) from [<c01885d8>] (kobject_add_internal+0x274/0x2fc)
[<c01885d8>] (kobject_add_internal) from [<c0188820>] (kobject_add+0x4c/0x98)
[<c0188820>] (kobject_add) from [<c01edacc>] (device_add+0xe0/0x4f0)
[<c01edacc>] (device_add) from [<c02559b0>] (of_platform_device_create_pdata+0x6c/0x8c)
[<c02559b0>] (of_platform_device_create_pdata) from [<c0255aac>] (of_platform_bus_create+0xd0/0x2b4)
[<c0255aac>] (of_platform_bus_create) from [<c0255db8>] (of_platform_populate+0x5c/0xa0)
[<c0255db8>] (of_platform_populate) from [<c0415fdc>] (customize_machine+0x20/0x44)
[<c0415fdc>] (customize_machine) from [<c0008b6c>] (do_one_initcall+0xfc/0x160)
[<c0008b6c>] (do_one_initcall) from [<c0413b40>] (kernel_init_freeable+0xf4/0x1ac)
[<c0413b40>] (kernel_init_freeable) from [<c0312b60>] (kernel_init+0x8/0xec)
[<c0312b60>] (kernel_init) from [<c0009830>] (ret_from_fork+0x14/0x24)
---[ end trace b6f453d64d825b4c ]---

After Linus' patch, the root is no longer soc0 so the fpga node's directory
becomes /devices/fpga while the attribute file remains at /devices/soc0/fpga.