linux-kernel - Re: [PATCH V1 Create empty OF root 1/1] of: create empty of root

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Date:   Fri, 11 Feb 2022 17:02:56 -0800
From:   Lizhi Hou <lizhi.hou@...inx.com>
To:     Xu Yilun <yilun.xu@...el.com>, Lizhi Hou <lizhi.hou@...inx.com>
CC:     <devicetree@...r.kernel.org>, <robh@...nel.org>,
        <linux-kernel@...r.kernel.org>, <maxz@...inx.com>,
        <sonal.santan@...inx.com>, <yliu@...inx.com>,
        <michal.simek@...inx.com>, <stefanos@...inx.com>,
        <trix@...hat.com>, <mdf@...nel.org>, <dwmw2@...radead.org>,
        Max Zhen <max.zhen@...inx.com>
Subject: Re: [PATCH V1 Create empty OF root 1/1] of: create empty of root

Hi Yilun,

Thanks a lot for your feedback. I will revise the comments and send 
another patch.

In the meanwhile, based on our previous discussion,

https://lore.kernel.org/lkml/20220111070000.GC979169@yilunxu-OptiPlex-7050/

I will propose another patch to add an of_pci interface which can be 
called by pci driver probe routine to create device node for it.


Thanks,

Lizhi

On 2/11/22 7:38 AM, Xu Yilun wrote:
> On Tue, Jan 25, 2022 at 09:48:07PM -0800, Lizhi Hou wrote:
>> Add OF_EMPTY_ROOT config. When it is selected and there is not a device
>> tree, create an empty device tree root node.
> Maybe add some description about why a empty device tree root node is
> needed. Note that the Patch #0 will not be present in the repo when the
> series will be merged, so add your description here please.
>
>> Signed-off-by: Sonal Santan <sonal.santan@...inx.com>
>> Signed-off-by: Max Zhen <max.zhen@...inx.com>
>> Signed-off-by: Lizhi Hou <lizhi.hou@...inx.com>
>> ---
>>   drivers/of/Kconfig         |  3 +++
>>   drivers/of/Makefile        |  1 +
>>   drivers/of/of_empty_root.c | 51 ++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 55 insertions(+)
>>   create mode 100644 drivers/of/of_empty_root.c
>>
>> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
>> index 80b5fd44ab1c..42afb126f91a 100644
>> --- a/drivers/of/Kconfig
>> +++ b/drivers/of/Kconfig
>> @@ -94,4 +94,7 @@ config OF_DMA_DEFAULT_COHERENT
>>   	# arches should select this if DMA is coherent by default for OF devices
>>   	bool
>>   
>> +config OF_EMPTY_ROOT
>> +	bool
> Also some descriptions for better understanding?
>
> Thanks,
> Yilun
>
>> +
>>   endif # OF
>> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
>> index e0360a44306e..c65364f32935 100644
>> --- a/drivers/of/Makefile
>> +++ b/drivers/of/Makefile
>> @@ -12,6 +12,7 @@ obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
>>   obj-$(CONFIG_OF_RESOLVE)  += resolver.o
>>   obj-$(CONFIG_OF_OVERLAY) += overlay.o
>>   obj-$(CONFIG_OF_NUMA) += of_numa.o
>> +obj-$(CONFIG_OF_EMPTY_ROOT) += of_empty_root.o
>>   
>>   ifdef CONFIG_KEXEC_FILE
>>   ifdef CONFIG_OF_FLATTREE
>> diff --git a/drivers/of/of_empty_root.c b/drivers/of/of_empty_root.c
>> new file mode 100644
>> index 000000000000..5c429c7a27bd
>> --- /dev/null
>> +++ b/drivers/of/of_empty_root.c
>> @@ -0,0 +1,51 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2022 Xilinx, Inc.
>> + */
>> +
>> +#include <linux/of.h>
>> +#include <linux/slab.h>
>> +
>> +#include "of_private.h"
>> +
>> +static int __init of_root_init(void)
>> +{
>> +	struct property *prop = NULL;
>> +	struct device_node *node;
>> +	__be32 *val = NULL;
>> +
>> +	if (of_root)
>> +		return 0;
>> +
>> +	pr_info("Create empty OF root node\n");
>> +	node = kzalloc(sizeof(*node), GFP_KERNEL);
>> +	if (!node)
>> +		return -ENOMEM;
>> +	of_node_init(node);
>> +	node->full_name = "/";
>> +
>> +	prop = kcalloc(2, sizeof(*prop), GFP_KERNEL);
>> +	if (!prop)
>> +		return -ENOMEM;
>> +
>> +	val = kzalloc(sizeof(*val), GFP_KERNEL);
>> +	if (!val)
>> +		return -ENOMEM;
>> +	*val = cpu_to_be32(sizeof(void *) / sizeof(u32));
>> +
>> +	prop->name = "#address-cells";
>> +	prop->value = val;
>> +	prop->length = sizeof(u32);
>> +	of_add_property(node, prop);
>> +	prop++;
>> +	prop->name = "#size-cells";
>> +	prop->value = val;
>> +	prop->length = sizeof(u32);
>> +	of_add_property(node, prop);
>> +	of_root = node;
>> +	for_each_of_allnodes(node)
>> +		__of_attach_node_sysfs(node);
>> +
>> +	return 0;
>> +}
>> +pure_initcall(of_root_init);
>> -- 
>> 2.27.0
>