Date:   Mon, 05 Jun 2017 21:43:06 +0300
From:   Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:     Stefani Seibold <stefani.seibold.ext@...wei.com>
Cc:     Stefani Seibold <stefani@...bold.net>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Holm Rauchfuss <holm.rauchfuss@...wei.com>
Subject: Re: [PATCH] external references for device tree overlays

Hi Stefani,

On Mon, 2017-06-05 at 14:59 +0200, Stefani Seibold wrote:
> From: Stefani Seibold <stefani@...bold.net>
> 
> This patch enables external references for symbols which are not
> exported by the current device tree. For example
> 
> // RASPI example (only for testing)
> /dts-v1/;
> /plugin/;
> 
> / {
>     compatible = "brcm,bcm2835", "brcm,bcm2708", "brcm,bcm2709";
> 
>     fragment@0 {
>         target-path = "/soc/i2s@...03000";
>         __overlay__ {
>             #address-cells = <0x00000001>;
>             #size-cells = <0x00000001>;
>             test = "test";
>             timer = <&timer>;
>         };
>     };
> 
>     __external_symbols__ {
>         timer = "/soc/timer@...03000";
>     };
> };
> 

I understand the problem. I am just not fond of the __external_symbols__
solution.

There's a facility in the DT source language that allows to declare
pathspec labels.

The 'timer = <&timer>;' statement could be rewritten as 
'timer = <&{/soc/timer@...030000}>;'

Internally you can 'catch' that this refers to a symbol in the base tree
and then do the same symbol insertion as the patch you've submitted.

The benefit to the above is that you don't introduce manually edited
special nodes.

Regards

-- Pantelis

> The "timer" symbol is not exported by the RASPI device tree, because it is
> missing in the __symbols__ section of the device tree.
> 
> In case of the RASPI device tree this could be simple fixed by modifing
> the device tree source, but when the device tree is provided by a closed
> source BIOS this kind of missing symbol could not be fixed.
> 
> An additional benefit is to override a (possible broken) symbol exported
> by the currect live device tree.
> 
> The patch is based and tested on linux 4.12-rc3.
> 
> Signed-off-by: Stefani Seibold <stefani.seibold.ext@...wei.com>
> Signed-off-by: Stefani Seibold <stefani@...bold.net>
> ---
>  drivers/of/overlay.c  | 19 +++++++++++++++++++
>  drivers/of/resolver.c | 27 ++++++++++++++++++++++-----
>  2 files changed, 41 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 7827786718d8..de6516ea0fcd 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -50,6 +50,7 @@ struct of_overlay {
>  	int id;
>  	struct list_head node;
>  	int count;
> +	struct device_node *tree;
>  	struct of_overlay_info *ovinfo_tab;
>  	struct of_changeset cset;
>  };
> @@ -422,6 +423,8 @@ int of_overlay_create(struct device_node *tree)
>  	/* add to the tail of the overlay list */
>  	list_add_tail(&ov->node, &ov_list);
>  
> +	ov->tree = tree;
> +
>  	of_overlay_notify(ov, OF_OVERLAY_POST_APPLY);
>  
>  	mutex_unlock(&of_mutex);
> @@ -524,6 +527,7 @@ int of_overlay_destroy(int id)
>  {
>  	struct of_overlay *ov;
>  	int err;
> +	phandle phandle;
>  
>  	mutex_lock(&of_mutex);
>  
> @@ -540,6 +544,8 @@ int of_overlay_destroy(int id)
>  		goto out;
>  	}
>  
> +	phandle = ov->tree->phandle;
> +
>  	of_overlay_notify(ov, OF_OVERLAY_PRE_REMOVE);
>  	list_del(&ov->node);
>  	__of_changeset_revert(&ov->cset);
> @@ -549,6 +555,19 @@ int of_overlay_destroy(int id)
>  	of_changeset_destroy(&ov->cset);
>  	kfree(ov);
>  
> +	if (phandle) {
> +		struct device_node *node;
> +		unsigned long flags;
> +
> +		raw_spin_lock_irqsave(&devtree_lock, flags);
> +		for_each_of_allnodes(node) {
> +			if (node->phandle >= phandle)
> +				node->phandle = 0;
> +		}
> +		raw_spin_unlock_irqrestore(&devtree_lock, flags);
> +	}
> +
> +
>  	err = 0;
>  
>  out:
> diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
> index 771f4844c781..31b5f32c9b27 100644
> --- a/drivers/of/resolver.c
> +++ b/drivers/of/resolver.c
> @@ -286,13 +286,14 @@ static int adjust_local_phandle_references(struct device_node *local_fixups,
>  int of_resolve_phandles(struct device_node *overlay)
>  {
>  	struct device_node *child, *local_fixups, *refnode;
> -	struct device_node *tree_symbols, *overlay_fixups;
> +	struct device_node *tree_symbols, *ext_symbols, *overlay_fixups;
>  	struct property *prop;
>  	const char *refpath;
>  	phandle phandle, phandle_delta;
>  	int err;
>  
>  	tree_symbols = NULL;
> +	ext_symbols = NULL;
>  
>  	if (!overlay) {
>  		pr_err("null overlay\n");
> @@ -321,6 +322,9 @@ int of_resolve_phandles(struct device_node *overlay)
>  	for_each_child_of_node(overlay, child) {
>  		if (!of_node_cmp(child->name, "__fixups__"))
>  			overlay_fixups = child;
> +		else
> +		if (!of_node_cmp(child->name, "__external_symbols__"))
> +			ext_symbols = child;
>  	}
>  
>  	if (!overlay_fixups) {
> @@ -329,20 +333,30 @@ int of_resolve_phandles(struct device_node *overlay)
>  	}
>  
>  	tree_symbols = of_find_node_by_path("/__symbols__");
> -	if (!tree_symbols) {
> -		pr_err("no symbols in root of device tree.\n");
> +	if (!tree_symbols && !ext_symbols) {
> +		pr_err("no symbols for resolve in device tree.\n");
>  		err = -EINVAL;
>  		goto out;
>  	}
>  
> +	phandle_delta = live_tree_max_phandle() + 1;
> +
>  	for_each_property_of_node(overlay_fixups, prop) {
>  
>  		/* skip properties added automatically */
>  		if (!of_prop_cmp(prop->name, "name"))
>  			continue;
>  
> -		err = of_property_read_string(tree_symbols,
> -				prop->name, &refpath);
> +		err = -1;
> +
> +		if (ext_symbols)
> +			err = of_property_read_string(ext_symbols,
> +					prop->name, &refpath);
> +
> +		if (err && tree_symbols)
> +			err = of_property_read_string(tree_symbols,
> +					prop->name, &refpath);
> +
>  		if (err)
>  			goto out;
>  
> @@ -352,6 +366,9 @@ int of_resolve_phandles(struct device_node *overlay)
>  			goto out;
>  		}
>  
> +		if (!refnode->phandle)
> +			refnode->phandle = ++phandle_delta;
> +
>  		phandle = refnode->phandle;
>  		of_node_put(refnode);
>  

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