Re: [PATCH] drivers/of: Fix depth for sub-tree blob in unflatten_dt_nodes()

[Gavin Shan <gwshan-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>]

On Wed, Jun 08, 2016 at 04:50:54PM +1000, Gavin Shan wrote:
>The function is unflattening device sub-tree blob if @dad passed to
>the function is valid. Currently, this functionality is used by PPC
>PowerNV PCI hotplug driver only. There are possibly multiple nodes
>in the first level of depth, fdt_next_node() bails immediately when
>@depth becomes negative before the second device node can be probed
>successfully. It leads to the device nodes except the first one won't
>be unflattened successfully.
>
>This fixes the issue by setting the initial depth (@inital_depth) to
>1 when this function is called to unflatten device sub-tree blob. No
>logic changes when this function is used to unflatten non-sub-tree
>blob.
>
>Cc: Rhyland Klein <rklein-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
>Fixes: 78c44d910 ("drivers/of: Fix depth when unflattening devicetree")
>Signed-off-by: Gavin Shan <gwshan-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
>---
> drivers/of/fdt.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>index 14f2f8c..9d70316 100644
>--- a/drivers/of/fdt.c
>+++ b/drivers/of/fdt.c
>@@ -395,7 +395,7 @@ static int unflatten_dt_nodes(const void *blob,
> 			      struct device_node **nodepp)
> {
> 	struct device_node *root;
>-	int offset = 0, depth = 0;
>+	int offset = 0, depth = 0, initial_depth = 0;
> #define FDT_MAX_DEPTH	64
> 	unsigned int fpsizes[FDT_MAX_DEPTH];
> 	struct device_node *nps[FDT_MAX_DEPTH];
>@@ -408,8 +408,19 @@ static int unflatten_dt_nodes(const void *blob,
> 	root = dad;
> 	fpsizes[depth] = dad ? strlen(of_node_full_name(dad)) : 0;
> 	nps[depth] = dad;
>+
>+	/*
>+	 * We're unflattening device sub-tree if @dad is valid. There are
>+	 * possibly multiple nodes in the first level of depth. We need
>+	 * set @depth to 1 to make fdt_next_node() happy as it bails
>+	 * immediately when negative @depth is found. Otherwise, the device
>+	 * nodes except the first one won't be unflattened successfully.
>+	 */
>+	if (dad)
>+		depth = initial_depth = 1;
>+

The change to @depth should happen before @fpsizes[depth] and @nps[depth]
are initialized. Otherwise, the parent device node and its full name length
are lost. It's why this didn't work for Andrew's hotplug case, but it did
work for me (with luck). I will post v2 to correct it.

Thanks,
Gavin

> 	for (offset = 0;
>-	     offset >= 0 && depth >= 0;
>+	     offset >= 0 && depth >= initial_depth;
> 	     offset = fdt_next_node(blob, offset, &depth)) {
> 		if (WARN_ON_ONCE(depth >= FDT_MAX_DEPTH))
> 			continue;
>-- 
>2.1.0
>

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