Le Thu, 23 Jun 2022 18:15:31 -0500,
Frank Rowand <frowand.list@xxxxxxxxx> 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@xxxxxxxxxx>
> > Signed-off-by: Rob Herring <robh@xxxxxxxxxx>
> > Signed-off-by: Clément Léger <clement.leger@xxxxxxxxxxx>
> > ---
> > 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
