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Message-ID: <8be0e1b7-92a9-f0ec-04ac-6946bd1d8103@gmail.com>
Date:   Thu, 23 Jun 2022 22:52:58 -0500
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Subject: Re: [PATCH v1 1/2] of: base: populate of_root node if not set
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From:   Frank Rowand <frowand.list@gmail.com>
To:     =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= <clement.leger@bootlin.com>,
        Rob Herring <robh+dt@kernel.org>
Cc:     linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        Lizhi Hou <lizhi.hou@xilinx.com>,
        Allan Nielsen <allan.nielsen@microchip.com>,
        Horatiu Vultur <horatiu.vultur@microchip.com>,
        Steen Hegelund <steen.hegelund@microchip.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Rob Herring <robh@kernel.org>
References: <20220623105044.152832-1-clement.leger@bootlin.com>
 <20220623105044.152832-2-clement.leger@bootlin.com>
 <ecf13de1-531f-b73b-b325-44ef78a3f818@gmail.com>
 <56822a64-f289-3b7d-2175-3669194587c9@gmail.com>
In-Reply-To: <56822a64-f289-3b7d-2175-3669194587c9@gmail.com>
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On 6/23/22 21:01, Frank Rowand wrote:
> On 6/23/22 19:15, Frank Rowand wrote:
>> Hi Clement,
>>
>> I said that I would send a patch to do this, but have failed to follow
>> through.  Sorry about that.
>>
>>
>> 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@kernel.org>
>>> Signed-off-by: Rob Herring <robh@kernel.org>
>>> Signed-off-by: Clément Léger <clement.leger@bootlin.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".
> 
> "a few minutes" is taking longer than expected.  One of the devicetree
> interrupt unittests is not giving the expected result for one of the
> configurations I am checking.

The test is ok.  The problem was unrelated asynchronous output to the
console intermingled with test output.

My suggested alternative patch series is at:

   https://lore.kernel.org/r/20220624034327.2542112-1-frowand.list@gmail.com

-Frank

> 
> -Frank
> 
>>
>> -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/;
>>> +
>>> +/ {
>>> +
>>> +};
>>
>