linux-kernel - Re: [PATCH V2 Create empty OF root 1/1] of: create empty of root

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Message-ID: <c7e4e7b9-c5e8-9af9-6c16-2a8e0e7e61f7@xilinx.com>
Date:   Tue, 17 May 2022 22:02:04 -0700
From:   Lizhi Hou <lizhi.hou@...inx.com>
To:     Frank Rowand <frowand.list@...il.com>,
        <devicetree@...r.kernel.org>, <robh@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <yilun.xu@...el.com>,
        <maxz@...inx.com>, <sonal.santan@...inx.com>, <larryliu@....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 V2 Create empty OF root 1/1] of: create empty of root


On 5/16/22 20:22, Frank Rowand wrote:
> CAUTION: This message has originated from an External Source. Please use proper judgment and caution when opening attachments, clicking links, or responding to this email.
>
>
> On 2/16/22 23:00, Lizhi Hou wrote:
>> Xilinx Alveo PCIe accelerator cards use flattened device tree to describe
>> describe apertures in its PCIe BARs. Each device tree node represents an
>> aperture and each aperture is an hardware unit which requires a driver.
>> The product detail:
>>      https://www.xilinx.com/products/boards-and-kits/alveo.html
>>
>> Thus a base device tree is required. Then the Alveo card driver can load
>> its flattened device tree and overlay it to the base tree. However device
>> tree does not always exist. To resolve this, add OF_EMPTY_ROOT config.
>> When it is selected and there is not a device tree, create an empty device
>> tree root node.
>>
> Please run scripts/get_maintainer on your patches to see who to put in
> the distribution list.
>
> I recently stumbled across this patch series and the previous related
> patch series (currently up to
> "[PATCH V3 XRT Alveo Infrastructure 0/8] XRT Alveo driver infrastructure overview")
> when I noticed it in an email archive.
Sorry about this. We will use scripts/get_maintainer to make sure the 
required maintainers are included next time.
>
> A similar need of creating an of_root if otherwise empty is being discussed
> in the thread "[PATCH 0/3] add dynamic PCI device of_node creation for overlay"
> at https://lore.kernel.org/r/20220427094502.456111-1-clement.leger@bootlin.com

Thanks a lot for your information. We investigated on adding dt node for 
PCI device as well and got some questions.

https://lore.kernel.org/lkml/79e4c876-e5a4-861f-cfbc-c75ed1a07ddd@xilinx.com/#t


Thanks,

Lizhi

>
> -Frank
>
>> 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         |  5 ++++
>>   drivers/of/Makefile        |  1 +
>>   drivers/of/of_empty_root.c | 51 ++++++++++++++++++++++++++++++++++++++
>>   3 files changed, 57 insertions(+)
>>   create mode 100644 drivers/of/of_empty_root.c
>>
>> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
>> index 80b5fd44ab1c..452d2316b47b 100644
>> --- a/drivers/of/Kconfig
>> +++ b/drivers/of/Kconfig
>> @@ -94,4 +94,9 @@ config OF_DMA_DEFAULT_COHERENT
>>        # arches should select this if DMA is coherent by default for OF devices
>>        bool
>>
>> +config OF_EMPTY_ROOT
>> +     # driver which requires at least the empty base device tree to
>> +     # overlay its own device nodes should select this.
>> +     bool
>> +
>>   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);