linux-kernel - Re: [PATCH V2 XRT Alveo Infrastructure 4/9] of: create empty of root

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Date:   Tue, 30 Nov 2021 13:21:49 -0800
From:   Lizhi Hou <lizhi.hou@...inx.com>
To:     Rob Herring <robh@...nel.org>, Lizhi Hou <lizhi.hou@...inx.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-fpga@...r.kernel.org>,
        <maxz@...inx.com>, <sonal.santan@...inx.com>, <yliu@...inx.com>,
        <michal.simek@...inx.com>, <stefanos@...inx.com>,
        <devicetree@...r.kernel.org>, <trix@...hat.com>, <mdf@...nel.org>,
        <dwmw2@...radead.org>, Max Zhen <max.zhen@...inx.com>
Subject: Re: [PATCH V2 XRT Alveo Infrastructure 4/9] of: create empty of root


On 11/29/21 5:59 PM, Rob Herring wrote:
> On Fri, Nov 19, 2021 at 02:24:07PM -0800, Lizhi Hou wrote:
>> When OF_FLATTREE is selected and there is not a device tree, create an
>> empty device tree root node. of/unittest.c code is referenced.
> What does the last sentence mean? You copied the code? If so, that's a
> sign you should refactor the unittest code to use this.

I looked into unittest.c for how the of_root is created.  And you are 
right, this could should be unified with unittest.c. I will change it 
with next patch set.

Thanks,

Lizhi

>
>> 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/Makefile        |  2 +-
>>   drivers/of/fdt.c           | 20 ++++++++++++++++++++
>>   drivers/of/fdt_default.dts |  5 +++++
>>   drivers/of/of_private.h    |  5 +++++
>>   4 files changed, 31 insertions(+), 1 deletion(-)
>>   create mode 100644 drivers/of/fdt_default.dts
>>
>> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
>> index c13b982084a3..815f5220465b 100644
>> --- a/drivers/of/Makefile
>> +++ b/drivers/of/Makefile
>> @@ -2,7 +2,7 @@
>>   obj-y = base.o device.o platform.o property.o
>>   obj-$(CONFIG_OF_KOBJ) += kobj.o
>>   obj-$(CONFIG_OF_DYNAMIC) += dynamic.o
>> -obj-$(CONFIG_OF_FLATTREE) += fdt.o
>> +obj-$(CONFIG_OF_FLATTREE) += fdt.o fdt_default.dtb.o
>>   obj-$(CONFIG_OF_EARLY_FLATTREE) += fdt_address.o
>>   obj-$(CONFIG_OF_PROMTREE) += pdt.o
>>   obj-$(CONFIG_OF_ADDRESS)  += address.o
>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>> index d64445e43ceb..3d6e4543419e 100644
>> --- a/drivers/of/fdt.c
>> +++ b/drivers/of/fdt.c
>> @@ -481,6 +481,26 @@ void *of_fdt_unflatten_tree(const unsigned long *blob,
>>   }
>>   EXPORT_SYMBOL_GPL(of_fdt_unflatten_tree);
>>
>> +static int __init of_fdt_root_init(void)
>> +{
>> +     struct device_node *np;
>> +
>> +     if (of_root)
>> +             return 0;
>> +
>> +     if (!of_fdt_unflatten_tree((const unsigned long *)__dtb_fdt_default_begin,
>> +                                NULL, &of_root)) {
>> +             pr_warn("%s: unflatten default tree failed\n", __func__);
>> +             return -ENODATA;
>> +     }
>> +
>> +     for_each_of_allnodes(np)
>> +             __of_attach_node_sysfs(np);
>> +
>> +     return 0;
>> +}
>> +late_initcall(of_fdt_root_init);
>> +
>>   /* Everything below here references initial_boot_params directly. */
>>   int __initdata dt_root_addr_cells;
>>   int __initdata dt_root_size_cells;
>> diff --git a/drivers/of/fdt_default.dts b/drivers/of/fdt_default.dts
>> new file mode 100644
>> index 000000000000..d1f12a76dfc6
>> --- /dev/null
>> +++ b/drivers/of/fdt_default.dts
>> @@ -0,0 +1,5 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/dts-v1/;
>> +
>> +/ {
>> +};
>> diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
>> index 631489f7f8c0..47c6bb47ef25 100644
>> --- a/drivers/of/of_private.h
>> +++ b/drivers/of/of_private.h
>> @@ -41,6 +41,11 @@ extern struct mutex of_mutex;
>>   extern struct list_head aliases_lookup;
>>   extern struct kset *of_kset;
>>
>> +#if defined(CONFIG_OF_FLATTREE)
>> +extern u8 __dtb_fdt_default_begin[];
>> +extern u8 __dtb_fdt_default_end[];
>> +#endif
>> +
>>   #if defined(CONFIG_OF_DYNAMIC)
>>   extern int of_property_notify(int action, struct device_node *np,
>>                              struct property *prop, struct property *old_prop);
>> --
>> 2.27.0
>>
>>