Patchwork [9/9] x86: OLPC: add OLPC device-tree support

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Submitter Andres Salomon
Date Aug. 30, 2010, 4:07 a.m.
Message ID <20100830000751.2b845d05@debxo>
Download mbox | patch
Permalink /patch/62994/
State Not Applicable
Delegated to: David Miller
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Comments

Andres Salomon - Aug. 30, 2010, 4:07 a.m.
Make use of PROC_DEVICETREE to export the tree, and sparc's PROMTREE code to
call into OLPC's Open Firmware to build the tree.

This also adds an init hook to proc_device_tree_init so that we can ensure
the device tree has been built prior to the proc_root_init stuff attempting
to populate /proc/device-tree.

Signed-off-by: Andres Salomon <dilinger@queued.net>
---
 arch/x86/Kconfig                |    2 +
 arch/x86/include/asm/olpc_ofw.h |    4 +
 arch/x86/include/asm/prom.h     |    1 +
 arch/x86/kernel/Makefile        |    1 +
 arch/x86/kernel/olpc_ofw.c      |    8 ++
 arch/x86/kernel/olpc_prom.c     |  152 +++++++++++++++++++++++++++++++++++++++
 drivers/of/pdt.c                |    2 +
 fs/proc/proc_devtree.c          |    4 +
 include/linux/of_pdt.h          |    1 +
 9 files changed, 175 insertions(+), 0 deletions(-)
 create mode 100644 arch/x86/include/asm/prom.h
 create mode 100644 arch/x86/kernel/olpc_prom.c
Grant Likely - Aug. 30, 2010, 6:14 p.m.
On Sun, Aug 29, 2010 at 10:07 PM, Andres Salomon <dilinger@queued.net> wrote:
>
> Make use of PROC_DEVICETREE to export the tree, and sparc's PROMTREE code to
> call into OLPC's Open Firmware to build the tree.
>
> This also adds an init hook to proc_device_tree_init so that we can ensure
> the device tree has been built prior to the proc_root_init stuff attempting
> to populate /proc/device-tree.

I'm not clear as to why this is needed.  I would expect OLPC platform
setup code would take care of extracting the device tree well before
the kernel gets to setting up the representation in /proc/device-tree.

g.

>
> Signed-off-by: Andres Salomon <dilinger@queued.net>
> ---
>  arch/x86/Kconfig                |    2 +
>  arch/x86/include/asm/olpc_ofw.h |    4 +
>  arch/x86/include/asm/prom.h     |    1 +
>  arch/x86/kernel/Makefile        |    1 +
>  arch/x86/kernel/olpc_ofw.c      |    8 ++
>  arch/x86/kernel/olpc_prom.c     |  152 +++++++++++++++++++++++++++++++++++++++
>  drivers/of/pdt.c                |    2 +
>  fs/proc/proc_devtree.c          |    4 +
>  include/linux/of_pdt.h          |    1 +
>  9 files changed, 175 insertions(+), 0 deletions(-)
>  create mode 100644 arch/x86/include/asm/prom.h
>  create mode 100644 arch/x86/kernel/olpc_prom.c
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index cea0cd9..7d4ef72 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2069,6 +2069,8 @@ config OLPC_OPENFIRMWARE
>        bool "Support for OLPC's Open Firmware"
>        depends on !X86_64 && !X86_PAE
>        default y if OLPC
> +       select OF
> +       select OF_PROMTREE
>        help
>          This option adds support for the implementation of Open Firmware
>          that is used on the OLPC XO-1 Children's Machine.
> diff --git a/arch/x86/include/asm/olpc_ofw.h b/arch/x86/include/asm/olpc_ofw.h
> index 08fde47..13075df 100644
> --- a/arch/x86/include/asm/olpc_ofw.h
> +++ b/arch/x86/include/asm/olpc_ofw.h
> @@ -28,4 +28,8 @@ static inline void setup_olpc_ofw_pgd(void) { }
>
>  #endif /* !CONFIG_OLPC_OPENFIRMWARE */
>
> +#ifdef CONFIG_PROC_DEVICETREE
> +extern void olpc_prom_build_devicetree(void);
> +#endif /* CONFIG_PROC_DEVICETREE */
> +
>  #endif /* _ASM_X86_OLPC_OFW_H */
> diff --git a/arch/x86/include/asm/prom.h b/arch/x86/include/asm/prom.h
> new file mode 100644
> index 0000000..b4ec95f
> --- /dev/null
> +++ b/arch/x86/include/asm/prom.h
> @@ -0,0 +1 @@
> +/* dummy prom.h; here to make linux/of.h's #includes happy */
> diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
> index 0925676..3d7e535 100644
> --- a/arch/x86/kernel/Makefile
> +++ b/arch/x86/kernel/Makefile
> @@ -105,6 +105,7 @@ scx200-y                    += scx200_32.o
>
>  obj-$(CONFIG_OLPC)             += olpc.o
>  obj-$(CONFIG_OLPC_OPENFIRMWARE)        += olpc_ofw.o
> +obj-$(CONFIG_PROC_DEVICETREE)  += olpc_prom.o
>  obj-$(CONFIG_X86_MRST)         += mrst.o
>
>  microcode-y                            := microcode_core.o
> diff --git a/arch/x86/kernel/olpc_ofw.c b/arch/x86/kernel/olpc_ofw.c
> index 3218aa7..6c4d243 100644
> --- a/arch/x86/kernel/olpc_ofw.c
> +++ b/arch/x86/kernel/olpc_ofw.c
> @@ -1,5 +1,7 @@
>  #include <linux/kernel.h>
>  #include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_pdt.h>
>  #include <linux/init.h>
>  #include <asm/page.h>
>  #include <asm/setup.h>
> @@ -38,6 +40,12 @@ void __init setup_olpc_ofw_pgd(void)
>        /* implicit optimization barrier here due to uninline function return */
>
>        early_iounmap(base, sizeof(olpc_ofw_pgd) * PTRS_PER_PGD);
> +
> +#ifdef CONFIG_PROC_DEVICETREE
> +       /* OFW set up succesfully; use it for the device tree */
> +       of_pdt_init_devicetree = olpc_prom_build_devicetree;
> +#endif
> +
>  }
>
>  int __olpc_ofw(const char *name, int nr_args, const void **args, int nr_res,
> diff --git a/arch/x86/kernel/olpc_prom.c b/arch/x86/kernel/olpc_prom.c
> new file mode 100644
> index 0000000..fb04d8a
> --- /dev/null
> +++ b/arch/x86/kernel/olpc_prom.c
> @@ -0,0 +1,152 @@
> +/*
> + * olpc_prom.c: OLPC-specific OFW device tree support code.
> + *
> + * Paul Mackerras      August 1996.
> + * Copyright (C) 1996-2005 Paul Mackerras.
> + *
> + *  Adapted for 64bit PowerPC by Dave Engebretsen and Peter Bergner.
> + *    {engebret|bergner}@us.ibm.com
> + *
> + *  Adapted for sparc by David S. Miller davem@davemloft.net
> + *  Adapted for x86/OLPC by Andres Salomon <dilinger@queued.net>
> + *
> + *      This program is free software; you can redistribute it and/or
> + *      modify it under the terms of the GNU General Public License
> + *      as published by the Free Software Foundation; either version
> + *      2 of the License, or (at your option) any later version.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/errno.h>
> +#include <linux/slab.h>
> +#include <linux/of.h>
> +#include <linux/of_pdt.h>
> +#include <asm/olpc_ofw.h>
> +
> +static phandle __init olpc_prom_getsibling(phandle node)
> +{
> +       const void *args[] = { (void *)node };
> +       void *res[] = { &node };
> +
> +       if (node == -1)
> +               return 0;
> +
> +       if (olpc_ofw("peer", args, res) || node == -1)
> +               return 0;
> +
> +       return node;
> +}
> +
> +static phandle __init olpc_prom_getchild(phandle node)
> +{
> +       const void *args[] = { (void *)node };
> +       void *res[] = { &node };
> +
> +       if (node == -1)
> +               return 0;
> +
> +       if (olpc_ofw("child", args, res) || node == -1) {
> +               pr_err("PROM: %s: fetching child failed!\n", __func__);
> +               return 0;
> +       }
> +
> +       return node;
> +}
> +
> +static int __init olpc_prom_getproplen(phandle node, const char *prop)
> +{
> +       const void *args[] = { (void *)node, prop };
> +       int len;
> +       void *res[] = { &len };
> +
> +       if (node == -1)
> +               return -1;
> +
> +       if (olpc_ofw("getproplen", args, res)) {
> +               pr_err("PROM: %s: getproplen failed!\n", __func__);
> +               return -1;
> +       }
> +
> +       return len;
> +}
> +
> +static int __init olpc_prom_getproperty(phandle node, const char *prop,
> +               char *buf, int bufsize)
> +{
> +       int plen;
> +
> +       plen = olpc_prom_getproplen(node, prop);
> +       if (plen > bufsize || plen < 1)
> +               return -1;
> +       else {
> +               const void *args[] = { (void *)node, prop, buf, (void *)plen };
> +               void *res[] = { &plen };
> +
> +               if (olpc_ofw("getprop", args, res)) {
> +                       pr_err("PROM: %s: getprop failed!\n", __func__);
> +                       return -1;
> +               }
> +       }
> +
> +       return plen;
> +}
> +
> +static int __init olpc_prom_nextprop(phandle node, const char *prev, char *buf)
> +{
> +       const void *args[] = { (void *)node, prev, buf };
> +       int success;
> +       void *res[] = { &success };
> +
> +       buf[0] = '\0';
> +
> +       if (node == -1)
> +               return -1;
> +
> +       if (olpc_ofw("nextprop", args, res) || success != 1)
> +               return -1;
> +
> +       return 0;
> +}
> +
> +static int __init olpc_prom_pkg2path(phandle node, char *buf,
> +               const int buflen, int *len)
> +{
> +       const void *args[] = { (void *)node, buf, (void *)buflen };
> +       void *res[] = { len };
> +
> +       if (node == -1)
> +               return -1;
> +
> +       if (olpc_ofw("package-to-path", args, res) || *len < 1)
> +               return -1;
> +
> +       return 0;
> +}
> +
> +void * __init prom_early_alloc(unsigned long size)
> +{
> +       /* this is called late enough that we can alloc normally */
> +       return kzalloc(size, GFP_KERNEL);
> +}
> +
> +static struct of_pdt_ops prom_olpc_ops __initdata = {
> +       .nextprop = olpc_prom_nextprop,
> +       .getproplen = olpc_prom_getproplen,
> +       .getproperty = olpc_prom_getproperty,
> +       .getchild = olpc_prom_getchild,
> +       .getsibling = olpc_prom_getsibling,
> +       .pkg2path = olpc_prom_pkg2path,
> +};
> +
> +void __init olpc_prom_build_devicetree(void)
> +{
> +       phandle root;
> +
> +       root = olpc_prom_getsibling(0);
> +       if (root < 0) {
> +               pr_err("PROM: unable to get root node from OFW!\n");
> +               return;
> +       }
> +       of_pdt_build_devicetree(root, &prom_olpc_ops);
> +}
> diff --git a/drivers/of/pdt.c b/drivers/of/pdt.c
> index 28295d0..07e3daa 100644
> --- a/drivers/of/pdt.c
> +++ b/drivers/of/pdt.c
> @@ -29,6 +29,8 @@ static struct of_pdt_ops *of_pdt_prom_ops __initdata;
>  void __initdata (*of_pdt_build_more)(struct device_node *dp,
>                struct device_node ***nextp);
>
> +void __initdata (*of_pdt_init_devicetree)(void);
> +
>  #if defined(CONFIG_SPARC)
>  unsigned int of_pdt_unique_id __initdata;
>
> diff --git a/fs/proc/proc_devtree.c b/fs/proc/proc_devtree.c
> index d9396a4..9779039 100644
> --- a/fs/proc/proc_devtree.c
> +++ b/fs/proc/proc_devtree.c
> @@ -11,6 +11,7 @@
>  #include <linux/stat.h>
>  #include <linux/string.h>
>  #include <linux/of.h>
> +#include <linux/of_pdt.h>
>  #include <linux/module.h>
>  #include <linux/slab.h>
>  #include <asm/prom.h>
> @@ -228,6 +229,9 @@ void __init proc_device_tree_init(void)
>  {
>        struct device_node *root;
>
> +       if (of_pdt_init_devicetree)
> +               of_pdt_init_devicetree();
> +
>        proc_device_tree = proc_mkdir("device-tree", NULL);
>        if (proc_device_tree == NULL)
>                return;
> diff --git a/include/linux/of_pdt.h b/include/linux/of_pdt.h
> index 9945e58..b4bd0ee 100644
> --- a/include/linux/of_pdt.h
> +++ b/include/linux/of_pdt.h
> @@ -38,6 +38,7 @@ extern void *prom_early_alloc(unsigned long size);
>
>  /* for building the device tree */
>  extern void of_pdt_build_devicetree(phandle root_node, struct of_pdt_ops *ops);
> +extern void (*of_pdt_init_devicetree)(void);
>
>  extern void (*of_pdt_build_more)(struct device_node *dp,
>                struct device_node ***nextp);
> --
> 1.5.6.5
>
>
Andres Salomon - Aug. 30, 2010, 6:49 p.m.
On Mon, 30 Aug 2010 12:14:57 -0600
Grant Likely <grant.likely@secretlab.ca> wrote:

> On Sun, Aug 29, 2010 at 10:07 PM, Andres Salomon
> <dilinger@queued.net> wrote:
> >
> > Make use of PROC_DEVICETREE to export the tree, and sparc's
> > PROMTREE code to call into OLPC's Open Firmware to build the tree.
> >
> > This also adds an init hook to proc_device_tree_init so that we can
> > ensure the device tree has been built prior to the proc_root_init
> > stuff attempting to populate /proc/device-tree.
> 
> I'm not clear as to why this is needed.  I would expect OLPC platform
> setup code would take care of extracting the device tree well before
> the kernel gets to setting up the representation in /proc/device-tree.
> 
> g.
> 

For simplicity; the OLPC platform setup code runs very early during
boot.  I preferred to keep that as minimal as possible, and defer
device tree allocation until the x86 mm code has finished initializing
(this skipping all the fun bootmem/etc work that'll be happening for
x86 soon).

Of course, once it's done initializing, one can either hardcode an
olpc_init_devtree call at the end of x86's setup_arch, or we can add a
generic hook for late devtree initialization right before proc
populates /proc/device-tree.  I chose the latter, but it could easily
be changed to the former if folks feel strongly about it.

I would've normally just used an initcall for it, but the proc_devtree
code runs prior to any of the initcall hooks.
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Grant Likely - Aug. 31, 2010, 5:49 a.m.
On Mon, Aug 30, 2010 at 12:49 PM, Andres Salomon <dilinger@queued.net> wrote:
> On Mon, 30 Aug 2010 12:14:57 -0600
> Grant Likely <grant.likely@secretlab.ca> wrote:
>
>> On Sun, Aug 29, 2010 at 10:07 PM, Andres Salomon
>> <dilinger@queued.net> wrote:
>> >
>> > Make use of PROC_DEVICETREE to export the tree, and sparc's
>> > PROMTREE code to call into OLPC's Open Firmware to build the tree.
>> >
>> > This also adds an init hook to proc_device_tree_init so that we can
>> > ensure the device tree has been built prior to the proc_root_init
>> > stuff attempting to populate /proc/device-tree.
>>
>> I'm not clear as to why this is needed.  I would expect OLPC platform
>> setup code would take care of extracting the device tree well before
>> the kernel gets to setting up the representation in /proc/device-tree.
>>
>> g.
>>
>
> For simplicity; the OLPC platform setup code runs very early during
> boot.  I preferred to keep that as minimal as possible, and defer
> device tree allocation until the x86 mm code has finished initializing
> (this skipping all the fun bootmem/etc work that'll be happening for
> x86 soon).
>
> Of course, once it's done initializing, one can either hardcode an
> olpc_init_devtree call at the end of x86's setup_arch, or we can add a
> generic hook for late devtree initialization right before proc
> populates /proc/device-tree.  I chose the latter, but it could easily
> be changed to the former if folks feel strongly about it.
>
> I would've normally just used an initcall for it, but the proc_devtree
> code runs prior to any of the initcall hooks.

Hmmm.  I wonder if proc_devtree initialization could be deferred to an
initcall.  That would make the problem go away.

g.
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Patch

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index cea0cd9..7d4ef72 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2069,6 +2069,8 @@  config OLPC_OPENFIRMWARE
 	bool "Support for OLPC's Open Firmware"
 	depends on !X86_64 && !X86_PAE
 	default y if OLPC
+	select OF
+	select OF_PROMTREE
 	help
 	  This option adds support for the implementation of Open Firmware
 	  that is used on the OLPC XO-1 Children's Machine.
diff --git a/arch/x86/include/asm/olpc_ofw.h b/arch/x86/include/asm/olpc_ofw.h
index 08fde47..13075df 100644
--- a/arch/x86/include/asm/olpc_ofw.h
+++ b/arch/x86/include/asm/olpc_ofw.h
@@ -28,4 +28,8 @@  static inline void setup_olpc_ofw_pgd(void) { }
 
 #endif /* !CONFIG_OLPC_OPENFIRMWARE */
 
+#ifdef CONFIG_PROC_DEVICETREE
+extern void olpc_prom_build_devicetree(void);
+#endif /* CONFIG_PROC_DEVICETREE */
+
 #endif /* _ASM_X86_OLPC_OFW_H */
diff --git a/arch/x86/include/asm/prom.h b/arch/x86/include/asm/prom.h
new file mode 100644
index 0000000..b4ec95f
--- /dev/null
+++ b/arch/x86/include/asm/prom.h
@@ -0,0 +1 @@ 
+/* dummy prom.h; here to make linux/of.h's #includes happy */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 0925676..3d7e535 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -105,6 +105,7 @@  scx200-y			+= scx200_32.o
 
 obj-$(CONFIG_OLPC)		+= olpc.o
 obj-$(CONFIG_OLPC_OPENFIRMWARE)	+= olpc_ofw.o
+obj-$(CONFIG_PROC_DEVICETREE)	+= olpc_prom.o
 obj-$(CONFIG_X86_MRST)		+= mrst.o
 
 microcode-y				:= microcode_core.o
diff --git a/arch/x86/kernel/olpc_ofw.c b/arch/x86/kernel/olpc_ofw.c
index 3218aa7..6c4d243 100644
--- a/arch/x86/kernel/olpc_ofw.c
+++ b/arch/x86/kernel/olpc_ofw.c
@@ -1,5 +1,7 @@ 
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_pdt.h>
 #include <linux/init.h>
 #include <asm/page.h>
 #include <asm/setup.h>
@@ -38,6 +40,12 @@  void __init setup_olpc_ofw_pgd(void)
 	/* implicit optimization barrier here due to uninline function return */
 
 	early_iounmap(base, sizeof(olpc_ofw_pgd) * PTRS_PER_PGD);
+
+#ifdef CONFIG_PROC_DEVICETREE
+	/* OFW set up succesfully; use it for the device tree */
+	of_pdt_init_devicetree = olpc_prom_build_devicetree;
+#endif
+
 }
 
 int __olpc_ofw(const char *name, int nr_args, const void **args, int nr_res,
diff --git a/arch/x86/kernel/olpc_prom.c b/arch/x86/kernel/olpc_prom.c
new file mode 100644
index 0000000..fb04d8a
--- /dev/null
+++ b/arch/x86/kernel/olpc_prom.c
@@ -0,0 +1,152 @@ 
+/*
+ * olpc_prom.c: OLPC-specific OFW device tree support code.
+ *
+ * Paul Mackerras	August 1996.
+ * Copyright (C) 1996-2005 Paul Mackerras.
+ *
+ *  Adapted for 64bit PowerPC by Dave Engebretsen and Peter Bergner.
+ *    {engebret|bergner}@us.ibm.com
+ *
+ *  Adapted for sparc by David S. Miller davem@davemloft.net
+ *  Adapted for x86/OLPC by Andres Salomon <dilinger@queued.net>
+ *
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; either version
+ *      2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_pdt.h>
+#include <asm/olpc_ofw.h>
+
+static phandle __init olpc_prom_getsibling(phandle node)
+{
+	const void *args[] = { (void *)node };
+	void *res[] = { &node };
+
+	if (node == -1)
+		return 0;
+
+	if (olpc_ofw("peer", args, res) || node == -1)
+		return 0;
+
+	return node;
+}
+
+static phandle __init olpc_prom_getchild(phandle node)
+{
+	const void *args[] = { (void *)node };
+	void *res[] = { &node };
+
+	if (node == -1)
+		return 0;
+
+	if (olpc_ofw("child", args, res) || node == -1) {
+		pr_err("PROM: %s: fetching child failed!\n", __func__);
+		return 0;
+	}
+
+	return node;
+}
+
+static int __init olpc_prom_getproplen(phandle node, const char *prop)
+{
+	const void *args[] = { (void *)node, prop };
+	int len;
+	void *res[] = { &len };
+
+	if (node == -1)
+		return -1;
+
+	if (olpc_ofw("getproplen", args, res)) {
+		pr_err("PROM: %s: getproplen failed!\n", __func__);
+		return -1;
+	}
+
+	return len;
+}
+
+static int __init olpc_prom_getproperty(phandle node, const char *prop,
+		char *buf, int bufsize)
+{
+	int plen;
+
+	plen = olpc_prom_getproplen(node, prop);
+	if (plen > bufsize || plen < 1)
+		return -1;
+	else {
+		const void *args[] = { (void *)node, prop, buf, (void *)plen };
+		void *res[] = { &plen };
+
+		if (olpc_ofw("getprop", args, res)) {
+			pr_err("PROM: %s: getprop failed!\n", __func__);
+			return -1;
+		}
+	}
+
+	return plen;
+}
+
+static int __init olpc_prom_nextprop(phandle node, const char *prev, char *buf)
+{
+	const void *args[] = { (void *)node, prev, buf };
+	int success;
+	void *res[] = { &success };
+
+	buf[0] = '\0';
+
+	if (node == -1)
+		return -1;
+
+	if (olpc_ofw("nextprop", args, res) || success != 1)
+		return -1;
+
+	return 0;
+}
+
+static int __init olpc_prom_pkg2path(phandle node, char *buf,
+		const int buflen, int *len)
+{
+	const void *args[] = { (void *)node, buf, (void *)buflen };
+	void *res[] = { len };
+
+	if (node == -1)
+		return -1;
+
+	if (olpc_ofw("package-to-path", args, res) || *len < 1)
+		return -1;
+
+	return 0;
+}
+
+void * __init prom_early_alloc(unsigned long size)
+{
+	/* this is called late enough that we can alloc normally */
+	return kzalloc(size, GFP_KERNEL);
+}
+
+static struct of_pdt_ops prom_olpc_ops __initdata = {
+	.nextprop = olpc_prom_nextprop,
+	.getproplen = olpc_prom_getproplen,
+	.getproperty = olpc_prom_getproperty,
+	.getchild = olpc_prom_getchild,
+	.getsibling = olpc_prom_getsibling,
+	.pkg2path = olpc_prom_pkg2path,
+};
+
+void __init olpc_prom_build_devicetree(void)
+{
+	phandle root;
+
+	root = olpc_prom_getsibling(0);
+	if (root < 0) {
+		pr_err("PROM: unable to get root node from OFW!\n");
+		return;
+	}
+	of_pdt_build_devicetree(root, &prom_olpc_ops);
+}
diff --git a/drivers/of/pdt.c b/drivers/of/pdt.c
index 28295d0..07e3daa 100644
--- a/drivers/of/pdt.c
+++ b/drivers/of/pdt.c
@@ -29,6 +29,8 @@  static struct of_pdt_ops *of_pdt_prom_ops __initdata;
 void __initdata (*of_pdt_build_more)(struct device_node *dp,
 		struct device_node ***nextp);
 
+void __initdata (*of_pdt_init_devicetree)(void);
+
 #if defined(CONFIG_SPARC)
 unsigned int of_pdt_unique_id __initdata;
 
diff --git a/fs/proc/proc_devtree.c b/fs/proc/proc_devtree.c
index d9396a4..9779039 100644
--- a/fs/proc/proc_devtree.c
+++ b/fs/proc/proc_devtree.c
@@ -11,6 +11,7 @@ 
 #include <linux/stat.h>
 #include <linux/string.h>
 #include <linux/of.h>
+#include <linux/of_pdt.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <asm/prom.h>
@@ -228,6 +229,9 @@  void __init proc_device_tree_init(void)
 {
 	struct device_node *root;
 
+	if (of_pdt_init_devicetree)
+		of_pdt_init_devicetree();
+
 	proc_device_tree = proc_mkdir("device-tree", NULL);
 	if (proc_device_tree == NULL)
 		return;
diff --git a/include/linux/of_pdt.h b/include/linux/of_pdt.h
index 9945e58..b4bd0ee 100644
--- a/include/linux/of_pdt.h
+++ b/include/linux/of_pdt.h
@@ -38,6 +38,7 @@  extern void *prom_early_alloc(unsigned long size);
 
 /* for building the device tree */
 extern void of_pdt_build_devicetree(phandle root_node, struct of_pdt_ops *ops);
+extern void (*of_pdt_init_devicetree)(void);
 
 extern void (*of_pdt_build_more)(struct device_node *dp,
 		struct device_node ***nextp);