Re: [PATCH v5 1/9] OF: Introduce Device Tree resolve support.

[Grant Likely]

On Wed, 28 May 2014 15:46:25 +0300, Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx> wrote:
> Introduce support for dynamic device tree resolution.
> Using it, it is possible to prepare a device tree that's
> been loaded on runtime to be modified and inserted at the kernel
> live tree.
> 
> Export of of_resolve and bug fix of double free by
> 	Guenter Roeck <groeck@xxxxxxxxxxx>
> 
> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
> ---
>  .../devicetree/dynamic-resolution-notes.txt        |  25 ++
>  drivers/of/Kconfig                                 |   6 +
>  drivers/of/Makefile                                |   1 +
>  drivers/of/resolver.c                              | 378 +++++++++++++++++++++
>  include/linux/of.h                                 |  17 +
>  5 files changed, 427 insertions(+)
>  create mode 100644 Documentation/devicetree/dynamic-resolution-notes.txt
>  create mode 100644 drivers/of/resolver.c
> 
> diff --git a/Documentation/devicetree/dynamic-resolution-notes.txt b/Documentation/devicetree/dynamic-resolution-notes.txt
> new file mode 100644
> index 0000000..0b396c4
> --- /dev/null
> +++ b/Documentation/devicetree/dynamic-resolution-notes.txt
> @@ -0,0 +1,25 @@
> +Device Tree Dynamic Resolver Notes
> +----------------------------------
> +
> +This document describes the implementation of the in-kernel
> +Device Tree resolver, residing in drivers/of/resolver.c and is a
> +companion document to Documentation/devicetree/dt-object-internal.txt[1]
> +
> +How the resolver works
> +----------------------
> +
> +The resolver is given as an input an arbitrary tree compiled with the
> +proper dtc option and having a /plugin/ tag. This generates the
> +appropriate __fixups__ & __local_fixups__ nodes as described in [1].
> +
> +In sequence the resolver works by the following steps:
> +
> +1. Get the maximum device tree phandle value from the live tree + 1.
> +2. Adjust all the local phandles of the tree to resolve by that amount.
> +3. Using the __local__fixups__ node information adjust all local references
> +   by the same amount.
> +4. For each property in the __fixups__ node locate the node it references
> +   in the live tree. This is the label used to tag the node.
> +5. Retrieve the phandle of the target of the fixup.
> +5. For each fixup in the property locate the node:property:offset location
> +   and replace it with the phandle value.
> diff --git a/drivers/of/Kconfig b/drivers/of/Kconfig
> index 2dcb054..0236a4e 100644
> --- a/drivers/of/Kconfig
> +++ b/drivers/of/Kconfig
> @@ -78,4 +78,10 @@ config OF_RESERVED_MEM
>  	help
>  	  Helpers to allow for reservation of memory regions
>  
> +config OF_RESOLVE
> +	bool
> +	depends on OF && !SPARC
> +	select OF_DYNAMIC
> +	select OF_DEVICE
> +
>  endmenu # OF
> diff --git a/drivers/of/Makefile b/drivers/of/Makefile
> index c62fc2a..27e3f29 100644
> --- a/drivers/of/Makefile
> +++ b/drivers/of/Makefile
> @@ -10,5 +10,6 @@ obj-$(CONFIG_OF_PCI)	+= of_pci.o
>  obj-$(CONFIG_OF_PCI_IRQ)  += of_pci_irq.o
>  obj-$(CONFIG_OF_MTD)	+= of_mtd.o
>  obj-$(CONFIG_OF_RESERVED_MEM) += of_reserved_mem.o
> +obj-$(CONFIG_OF_RESOLVE)  += resolver.o
>  
>  CFLAGS_fdt.o = -I$(src)/../../scripts/dtc/libfdt
> diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
> new file mode 100644
> index 0000000..cbf4180
> --- /dev/null
> +++ b/drivers/of/resolver.c
> @@ -0,0 +1,378 @@
> +/*
> + * Functions for dealing with DT resolution
> + *
> + * Copyright (C) 2012 Pantelis Antoniou <panto@xxxxxxxxxxxxxxxxxxxxxxx>
> + * Copyright (C) 2012 Texas Instruments Inc.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * version 2 as published by the Free Software Foundation.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/string.h>
> +#include <linux/ctype.h>
> +#include <linux/errno.h>
> +#include <linux/string.h>
> +#include <linux/slab.h>
> +
> +/*
> + * Find live tree's maximum phandle value.
> + */
> +static phandle of_get_tree_max_phandle(void)
> +{
> +	struct device_node *node;
> +	phandle phandle;
> +	unsigned long flags;
> +
> +	/* now search recursively */
> +	raw_spin_lock_irqsave(&devtree_lock, flags);
> +	phandle = 0;
> +	for_each_of_allnodes(node) {
> +		if (node->phandle != OF_PHANDLE_ILLEGAL &&
> +				node->phandle > phandle)
> +			phandle = node->phandle;
> +	}
> +	raw_spin_unlock_irqrestore(&devtree_lock, flags);
> +
> +	return phandle;
> +}

It will be important to hold the tree modification mutex while
resolving an overlay. If two overlays are in flight it could cause
collisions.

> +
> +/*
> + * Adjust a subtree's phandle values by a given delta.
> + * Makes sure not to just adjust the device node's phandle value,
> + * but modify the phandle properties values as well.
> + */
> +static void __of_adjust_tree_phandles(struct device_node *node,
> +		int phandle_delta)
> +{
> +	struct device_node *child;
> +	struct property *prop;
> +	phandle phandle;
> +
> +	/* first adjust the node's phandle direct value */
> +	if (node->phandle != 0 && node->phandle != OF_PHANDLE_ILLEGAL)
> +		node->phandle += phandle_delta;
> +
> +	/* now adjust phandle & linux,phandle values */
> +	for_each_property_of_node(node, prop) {
> +
> +		/* only look for these two */
> +		if (of_prop_cmp(prop->name, "phandle") != 0 &&
> +		    of_prop_cmp(prop->name, "linux,phandle") != 0)
> +			continue;
> +
> +		/* must be big enough */
> +		if (prop->length < 4)
> +			continue;
> +
> +		/* read phandle value */
> +		phandle = be32_to_cpup(prop->value);
> +		if (phandle == OF_PHANDLE_ILLEGAL)	/* unresolved */
> +			continue;
> +
> +		/* adjust */
> +		*(uint32_t *)prop->value = cpu_to_be32(node->phandle);
> +	}
> +
> +	/* now do the children recursively */
> +	__for_each_child_of_node(node, child)
> +		__of_adjust_tree_phandles(child, phandle_delta);
> +}

Instead of recursion, use an allnodes loop:

	for (; node; node = node->allnext) {
		...
	}

> +
> +/*
> + * Adjust the local phandle references by the given phandle delta.
> + * Assumes the existances of a __local_fixups__ node at the root
> + * of the tree. Does not take any devtree locks so make sure you
> + * call this on a tree which is at the detached state.
> + */
> +static int __of_adjust_tree_phandle_references(struct device_node *node,
> +		int phandle_delta)
> +{
> +	phandle phandle;
> +	struct device_node *refnode, *child;
> +	struct property *rprop, *sprop;
> +	char *propval, *propcur, *propend, *nodestr, *propstr, *s;
> +	int offset, propcurlen;
> +	int err;
> +
> +	/* locate the symbols & fixups nodes on resolve */
> +	__for_each_child_of_node(node, child)
> +		if (of_node_cmp(child->name, "__local_fixups__") == 0)
> +			break;
> +
> +	/* no local fixups */
> +	if (!child)
> +		return 0;
> +
> +	/* find the local fixups property */
> +	for_each_property_of_node(child, rprop) {
> +
> +		/* skip properties added automatically */
> +		if (of_prop_cmp(rprop->name, "name") == 0)
> +			continue;
> +
> +		/* make a copy */
> +		propval = kmalloc(rprop->length, GFP_KERNEL);
> +		if (!propval) {
> +			pr_err("%s: Could not copy value of '%s'\n",
> +					__func__, rprop->name);
> +			return -ENOMEM;
> +		}
> +		memcpy(propval, rprop->value, rprop->length);

kmemdup(). I think the parsing can be made more elegant to not require
the copy, but that can be a future enhancement. There isn't anything
incorrect here.

We could just modify the property value in-place since this property is
never used again after the tree has been resolved.

> +		propend = propval + rprop->length;
> +		for (propcur = propval; propcur < propend;
> +				propcur += propcurlen + 1) {
> +
> +			propcurlen = strlen(propcur);

Need a check here to make sure the current string doesn't overrun
propend. The for loop only checks if the start of the string overruns,
not the end.

> +
> +			nodestr = propcur;
> +			s = strchr(propcur, ':');
> +			if (!s) {
> +				pr_err("%s: Illegal symbol entry '%s' (1)\n",
> +					__func__, propcur);
> +				err = -EINVAL;
> +				goto err_fail;
> +			}
> +			*s++ = '\0';
> +
> +			propstr = s;
> +			s = strchr(s, ':');
> +			if (!s) {
> +				pr_err("%s: Illegal symbol entry '%s' (2)\n",
> +					__func__, (char *)rprop->value);
> +				err = -EINVAL;
> +				goto err_fail;
> +			}
> +
> +			*s++ = '\0';
> +			err = kstrtoint(s, 10, &offset);
> +			if (err != 0) {
> +				pr_err("%s: Could get offset '%s'\n",
> +					__func__, (char *)rprop->value);
> +				goto err_fail;
> +			}
> +
> +			/* look into the resolve node for the full path */
> +			refnode = __of_find_node_by_full_name(node, nodestr);
> +			if (!refnode) {
> +				pr_warn("%s: Could not find refnode '%s'\n",
> +					__func__, (char *)rprop->value);
> +				continue;
> +			}
> +
> +			/* now find the property */
> +			for_each_property_of_node(refnode, sprop) {
> +				if (of_prop_cmp(sprop->name, propstr) == 0)
> +					break;
> +			}
> +
> +			if (!sprop) {
> +				pr_err("%s: Could not find property '%s'\n",
> +					__func__, (char *)rprop->value);
> +				err = -ENOENT;
> +				goto err_fail;
> +			}
> +
> +			phandle = be32_to_cpup(sprop->value + offset);
> +			*(__be32 *)(sprop->value + offset) =
> +				cpu_to_be32(phandle + phandle_delta);
> +		}
> +
> +		kfree(propval);
> +		propval = NULL;
> +	}
> +
> +	return 0;
> +
> +err_fail:
> +	kfree(propval);
> +	return err;
> +}
> +
> +/**
> + * of_resolve	- Resolve the given node against the live tree.
> + *
> + * @resolve:	Node to resolve
> + *
> + * Perform dynamic Device Tree resolution against the live tree
> + * to the given node to resolve. This depends on the live tree
> + * having a __symbols__ node, and the resolve node the __fixups__ &
> + * __local_fixups__ nodes (if needed).

Is the above still true? I thought the __symbols__ node was obsolete

> + * The result of the operation is a resolve node that it's contents
> + * are fit to be inserted or operate upon the live tree.
> + * Returns 0 on success or a negative error value on error.

Include comment that need to hold the tree modification mutex when
calling this code.

Overall the code looks good. I might pick this one up for merging. If I
do then you can send fixup patches to resolve the comments above.

g.

> + */
> +int of_resolve(struct device_node *resolve)
> +{
> +	struct device_node *child, *refnode;
> +	struct device_node *root_sym, *resolve_sym, *resolve_fix;
> +	struct property *rprop, *sprop;
> +	const char *refpath;
> +	char *propval, *propcur, *propend, *nodestr, *propstr, *s;
> +	int offset, propcurlen;
> +	phandle phandle, phandle_delta;
> +	int err;
> +
> +	/* the resolve node must exist, and be detached */
> +	if (!resolve || !of_node_check_flag(resolve, OF_DETACHED))
> +		return -EINVAL;
> +
> +	/* first we need to adjust the phandles */
> +	phandle_delta = of_get_tree_max_phandle() + 1;
> +	__of_adjust_tree_phandles(resolve, phandle_delta);
> +	err = __of_adjust_tree_phandle_references(resolve, phandle_delta);
> +	if (err != 0)
> +		return err;
> +
> +	root_sym = NULL;
> +	resolve_sym = NULL;
> +	resolve_fix = NULL;
> +
> +	/* this may fail (if no fixups are required) */
> +	root_sym = of_find_node_by_path("/__symbols__");
> +
> +	/* locate the symbols & fixups nodes on resolve */
> +	__for_each_child_of_node(resolve, child) {
> +
> +		if (!resolve_sym &&
> +				of_node_cmp(child->name, "__symbols__") == 0)
> +			resolve_sym = child;
> +
> +		if (!resolve_fix &&
> +				of_node_cmp(child->name, "__fixups__") == 0)
> +			resolve_fix = child;
> +
> +		/* both found, don't bother anymore */
> +		if (resolve_sym && resolve_fix)
> +			break;
> +	}
> +
> +	/* we do allow for the case where no fixups are needed */
> +	if (!resolve_fix) {
> +		err = 0;	/* no error */
> +		goto out;
> +	}
> +
> +	/* we need to fixup, but no root symbols... */
> +	if (!root_sym) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> +	for_each_property_of_node(resolve_fix, rprop) {
> +
> +		/* skip properties added automatically */
> +		if (of_prop_cmp(rprop->name, "name") == 0)
> +			continue;
> +
> +		err = of_property_read_string(root_sym,
> +				rprop->name, &refpath);
> +		if (err != 0) {
> +			pr_err("%s: Could not find symbol '%s'\n",
> +					__func__, rprop->name);
> +			goto out;
> +		}
> +
> +		refnode = of_find_node_by_path(refpath);
> +		if (!refnode) {
> +			pr_err("%s: Could not find node by path '%s'\n",
> +					__func__, refpath);
> +			err = -ENOENT;
> +			goto out;
> +		}
> +
> +		phandle = refnode->phandle;
> +		of_node_put(refnode);
> +
> +		pr_debug("%s: %s phandle is 0x%08x\n",
> +				__func__, rprop->name, phandle);
> +
> +		/* make a copy */
> +		propval = kmalloc(rprop->length, GFP_KERNEL);
> +		if (!propval) {
> +			pr_err("%s: Could not copy value of '%s'\n",
> +					__func__, rprop->name);
> +			err = -ENOMEM;
> +			goto out;
> +		}
> +
> +		memcpy(propval, rprop->value, rprop->length);
> +
> +		propend = propval + rprop->length;
> +		for (propcur = propval; propcur < propend;
> +				propcur += propcurlen + 1) {
> +			propcurlen = strlen(propcur);
> +
> +			nodestr = propcur;
> +			s = strchr(propcur, ':');
> +			if (!s) {
> +				pr_err("%s: Illegal symbol entry '%s' (1)\n",
> +					__func__, (char *)rprop->value);
> +				err = -EINVAL;
> +				goto err_fail_free;
> +			}
> +			*s++ = '\0';
> +
> +			propstr = s;
> +			s = strchr(s, ':');
> +			if (!s) {
> +				pr_err("%s: Illegal symbol entry '%s' (2)\n",
> +					__func__, (char *)rprop->value);
> +				err = -EINVAL;
> +				goto err_fail_free;
> +			}
> +
> +			*s++ = '\0';
> +			err = kstrtoint(s, 10, &offset);
> +			if (err != 0) {
> +				pr_err("%s: Could get offset '%s'\n",
> +					__func__, (char *)rprop->value);
> +				goto err_fail_free;
> +			}
> +
> +			/* look into the resolve node for the full path */
> +			refnode = __of_find_node_by_full_name(resolve,
> +					nodestr);
> +			if (!refnode) {
> +				pr_err("%s: Could not find refnode '%s'\n",
> +					__func__, (char *)rprop->value);
> +				err = -ENOENT;
> +				goto err_fail_free;
> +			}
> +
> +			/* now find the property */
> +			for_each_property_of_node(refnode, sprop) {
> +				if (of_prop_cmp(sprop->name, propstr) == 0)
> +					break;
> +			}
> +
> +			if (!sprop) {
> +				pr_err("%s: Could not find property '%s'\n",
> +					__func__, (char *)rprop->value);
> +				err = -ENOENT;
> +				goto err_fail_free;
> +			}
> +
> +			*(__be32 *)(sprop->value + offset) =
> +				cpu_to_be32(phandle);
> +		}
> +
> +		kfree(propval);
> +		propval = NULL;
> +	}
> +
> +err_fail_free:
> +	kfree(propval);
> +
> +out:
> +	/* NULL is handled by of_node_put as NOP */
> +	of_node_put(root_sym);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(of_resolve);
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 29113d3..9d5795c 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -823,4 +823,21 @@ static inline struct device_node *__of_create_empty_node( const char *name,
>  
>  #endif	/* !CONFIG_OF */
>  
> +
> +/* illegal phandle value (set when unresolved) */
> +#define OF_PHANDLE_ILLEGAL	0xdeadbeef
> +
> +#ifdef CONFIG_OF_RESOLVE
> +
> +int of_resolve(struct device_node *resolve);
> +
> +#else
> +
> +static inline int of_resolve(struct device_node *resolve)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +#endif
> +
>  #endif /* _LINUX_OF_H */
> -- 
> 1.7.12
> 
> --
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