linux-kernel - Re: [PATCH v1 1/2] of: base: populate of

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Date:   Fri, 24 Jun 2022 14:04:15 +0200
From:   Clément Léger <clement.leger@...tlin.com>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Rob Herring <robh+dt@...nel.org>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, Lizhi Hou <lizhi.hou@...inx.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v1 1/2] of: base: populate of_root node if not set

Le Thu, 23 Jun 2022 18:15:31 -0500,
Frank Rowand <frowand.list@...il.com> a écrit :

> Hi Clement,
> 
> I said that I would send a patch to do this, but have failed to follow
> through.  Sorry about that.

Hi Frank, no worries, I just needed this topic to move forward, that's
why I decided to sent this .

Thanks !

Clément

> 
> 
> On 6/23/22 06:50, Clément Léger wrote:
> > When enabling CONFIG_OF on a platform where of_root is not populated by
> > firmware, we end up without a root node. In order to apply overlays and
> > create subnodes of the root node, we need one. Create this root node
> > by unflattening an empty builtin dtb with of_fdt_unflatten().
> > 
> > Co-developed-by: Rob Herring <robh@...nel.org>
> > Signed-off-by: Rob Herring <robh@...nel.org>
> > Signed-off-by: Clément Léger <clement.leger@...tlin.com>
> > ---
> >  drivers/of/Makefile       |  2 +-
> >  drivers/of/base.c         | 18 ++++++++++++++++--
> >  drivers/of/empty_root.dts |  6 ++++++
> >  3 files changed, 23 insertions(+), 3 deletions(-)
> >  create mode 100644 drivers/of/empty_root.dts
> > 
> > diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> > index e0360a44306e..ce56c8b95c83 100644
> > --- a/drivers/of/Makefile
> > +++ b/drivers/of/Makefile
> > @@ -1,5 +1,5 @@
> >  # SPDX-License-Identifier: GPL-2.0
> > -obj-y = base.o device.o platform.o property.o
> > +obj-y = base.o empty_root.dtb.o device.o platform.o property.o
> >  obj-$(CONFIG_OF_KOBJ) += kobj.o
> >  obj-$(CONFIG_OF_DYNAMIC) += dynamic.o
> >  obj-$(CONFIG_OF_FLATTREE) += fdt.o
> > diff --git a/drivers/of/base.c b/drivers/of/base.c
> > index d4f98c8469ed..43e0f027a49c 100644
> > --- a/drivers/of/base.c
> > +++ b/drivers/of/base.c
> > @@ -22,6 +22,7 @@
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> >  #include <linux/of_device.h>
> > +#include <linux/of_fdt.h>
> >  #include <linux/of_graph.h>
> >  #include <linux/spinlock.h>
> >  #include <linux/slab.h>
> > @@ -163,6 +164,8 @@ void __of_phandle_cache_inv_entry(phandle handle)
> >  		phandle_cache[handle_hash] = NULL;
> >  }
> >  
> > +extern const char __dtb_empty_root_begin[];
> > +
> >  void __init of_core_init(void)
> >  {
> >  	struct device_node *np;
> > @@ -176,6 +179,18 @@ void __init of_core_init(void)
> >  		pr_err("failed to register existing nodes\n");
> >  		return;
> >  	}
> > +
> > +	if (!of_root) {
> > +		void *dt;
> > +		const unsigned long *fdt = (const unsigned long *)
> > +							__dtb_empty_root_begin;
> > +		dt = of_fdt_unflatten_tree(fdt, NULL, &of_root);
> > +		if (!dt) {
> > +			pr_err("Failed to setup empty root dt\n");
> > +			return;
> > +		}
> > +	}
> > +
> >  	for_each_of_allnodes(np) {
> >  		__of_attach_node_sysfs(np);
> >  		if (np->phandle && !phandle_cache[of_phandle_cache_hash(np->phandle)])
> > @@ -184,8 +199,7 @@ void __init of_core_init(void)
> >  	mutex_unlock(&of_mutex);
> >  
> >  	/* Symlink in /proc as required by userspace ABI */
> > -	if (of_root)
> > -		proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
> > +	proc_symlink("device-tree", NULL, "/sys/firmware/devicetree/base");
> >  }  
> 
> This approach is adding an additional method of unflattening the tree.
> I would prefer to consolidate in a single location.
> 
> I have leveraged this patch series into a different patch series to
> accomplish that.  I have boot tested with one configuration, but want
> to test two more configurations before sending the new series.  It
> should only take "a few minutes".
> 
> -Frank
> 
> >  
> >  static struct property *__of_find_property(const struct device_node *np,
> > diff --git a/drivers/of/empty_root.dts b/drivers/of/empty_root.dts
> > new file mode 100644
> > index 000000000000..cf9e97a60f48
> > --- /dev/null
> > +++ b/drivers/of/empty_root.dts
> > @@ -0,0 +1,6 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/dts-v1/;
> > +
> > +/ {
> > +
> > +};  
> 



-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com