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SubjectRe: [PATCH V2 Create empty OF root 1/1] of: create empty of root
From
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.

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

-Frank

> Signed-off-by: Sonal Santan <sonal.santan@xilinx.com>
> Signed-off-by: Max Zhen <max.zhen@xilinx.com>
> Signed-off-by: Lizhi Hou <lizhi.hou@xilinx.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);

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