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