[RFC PATCH 1/5] dt: Provide a way to remove non-compliant nodes and properties

[Heinrich Schuchardt]

On 8/26/23 11:06, Sughosh Ganu wrote:
> Add a function which is registered to spy for a EVT_FT_FIXUP event,
> and removes the non upstreamed nodes and properties from the
> devicetree before it gets passed to the OS.
>
> This allows removing entire nodes, or specific properties under nodes
> from the devicetree. The required nodes and properties can be
> registered for removal through the DT_NON_COMPLIANT_PURGE and
> DT_NON_COMPLIANT_PURGE_LIST macros.
>
> Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
> ---
>   include/dt-structs.h | 11 +++++++
>   lib/Makefile         |  1 +
>   lib/dt_purge.c       | 73 ++++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 85 insertions(+)
>   create mode 100644 lib/dt_purge.c
>
> diff --git a/include/dt-structs.h b/include/dt-structs.h
> index fa1622cb1d..f535c60471 100644
> --- a/include/dt-structs.h
> +++ b/include/dt-structs.h
> @@ -57,3 +57,14 @@ struct phandle_2_arg {
>   #endif
>
>   #endif
> +
> +struct dt_non_compliant_purge {
> +	const char *node_path;
> +	const char *prop;
> +};
> +
> +#define DT_NON_COMPLIANT_PURGE(__name)	\
> +	ll_entry_declare(struct dt_non_compliant_purge, __name, dt_purge)
> +
> +#define DT_NON_COMPLIANT_PURGE_LIST(__name)	\
> +	ll_entry_declare_list(struct dt_non_compliant_purge, __name, dt_purge)
> diff --git a/lib/Makefile b/lib/Makefile
> index 8d8ccc8bbc..82a906daa0 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -37,6 +37,7 @@ endif
>   obj-y += crc8.o
>   obj-y += crc16.o
>   obj-y += crc16-ccitt.o
> +obj-y += dt_purge.o
>   obj-$(CONFIG_ERRNO_STR) += errno_str.o
>   obj-$(CONFIG_FIT) += fdtdec_common.o
>   obj-$(CONFIG_TEST_FDTDEC) += fdtdec_test.o
> diff --git a/lib/dt_purge.c b/lib/dt_purge.c
> new file mode 100644
> index 0000000000..f893ba9796
> --- /dev/null
> +++ b/lib/dt_purge.c
> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (c) 2023, Linaro Limited
> + */
> +
> +#include <dt-structs.h>
> +#include <event.h>
> +#include <linker_lists.h>
> +
> +#include <linux/libfdt.h>
> +
> +/**
> + * dt_non_compliant_purge() -	Remove non-upstreamed nodes and properties
> + *				from the DT
> + * @ctx: Context for event
> + * @event: Event to process
> + *
> + * Iterate through an array of DT nodes and properties, and remove them
> + * from the device-tree before the DT gets handed over to the kernel.
> + * These are nodes and properties which do not have upstream bindings
> + * and need to be purged before being handed over to the kernel.
> + *
> + * If both the node and property are specified, delete the property. If
> + * only the node is specified, delete the entire node, including it's
> + * subnodes, if any.
> + *
> + * Return: 0 if OK, -ve on error
> + */
> +static int dt_non_compliant_purge(void *ctx, struct event *event)
> +{
> +	int nodeoff = 0;
> +	int err = 0;
> +	void *fdt;
> +	const struct event_ft_fixup *fixup = &event->data.ft_fixup;
> +	struct dt_non_compliant_purge *purge_entry;
> +	struct dt_non_compliant_purge *purge_start =
> +		ll_entry_start(struct dt_non_compliant_purge, dt_purge);
> +	int nentries = ll_entry_count(struct dt_non_compliant_purge, dt_purge);
> +
> +	if (fixup->images)
> +		return 0;
> +
> +	fdt = fixup->tree.fdt;
> +	for (purge_entry = purge_start; purge_entry != purge_start + nentries;
> +	     purge_entry++) {
> +		nodeoff = fdt_path_offset(fdt, purge_entry->node_path);
> +		if (nodeoff < 0) {
> +			log_debug("Error (%d) getting node offset for %s\n",
> +				  nodeoff, purge_entry->node_path);
> +			continue;
> +		}
> +
> +		if (purge_entry->prop) {
> +			err = fdt_delprop(fdt, nodeoff, purge_entry->prop);
> +			if (err < 0 && err != -FDT_ERR_NOTFOUND) {
> +				log_debug("Error (%d) deleting %s\n",
> +					  err, purge_entry->prop);
> +				goto out;
> +			}
> +		} else {
> +			err = fdt_del_node(fdt, nodeoff);
> +			if (err) {
> +				log_debug("Error (%d) trying to delete node %s\n",
> +					  err, purge_entry->node_path);
> +				goto out;
> +			}
> +		}
> +	}
> +
> +out:
> +	return err;
> +}
> +EVENT_SPY(EVT_FT_FIXUP, dt_non_compliant_purge);

This may interfere with other fixup code requiring U-Boot specific
properties like bootmeth_vbe_ft_fixup().

We should ensure that call dt_non_compliant_purge() is the last fixup
action. Please, consider a separate event.

This code does not check if the property or node complies to the device
tree scheme or not. So why not call the function dt_purge()?

Best regards

Heinrich