of/fdt: skip unflattening of disabled nodes

For static DT usecases, we don't need the disabled nodes and can skip
unflattening. This saves a significant amount of RAM in memory constrained
cases. In one example on STM32F469, the RAM usage goes from 118K to 26K.

There are a few cases in the kernel that modify the status property
dynamically. These all are changes from enabled to disabled, depend on
OF_DYNAMIC or are not FDT based (PDT based).

Tested-by: Nicolas Pitre <nico@linaro.org>
Reviewed-by: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Rob Herring <robh@kernel.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index f8c39705418b..2d515b85a198 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -396,6 +396,10 @@ static int unflatten_dt_nodes(const void *blob,
                 if (WARN_ON_ONCE(depth >= FDT_MAX_DEPTH))
                         continue;
 
+                if (!IS_ENABLED(CONFIG_OF_KOBJ) &&
+                    !of_fdt_device_is_available(blob, offset))
+                        continue;
+
                 if (!populate_node(blob, offset, &mem, nps[depth],
                                    &nps[depth+1], dryrun))
                         return mem - base;