linux-kernel - [PATCH 2/2] of/fdt: skip unflattening of disabled nodes

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Date:   Tue,  3 Oct 2017 11:18:15 -0500
From:   Rob Herring <robh@...nel.org>
To:     devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Frank Rowand <frowand.list@...il.com>
Subject: [PATCH 2/2] 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).

Cc: Nicolas Pitre <nicolas.pitre@...aro.org>
Cc: Frank Rowand <frowand.list@...il.com>
Signed-off-by: Rob Herring <robh@...nel.org>
---
For more background, see this presentation from Nico:

https://connect.linaro.org/resource/sfo17/sfo17-100/

 drivers/of/fdt.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index f8c39705418b..efe91c6856a0 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_DYNAMIC) &&
+		    !of_fdt_device_is_available(blob, offset))
+			continue;
+
 		if (!populate_node(blob, offset, &mem, nps[depth],
 				   &nps[depth+1], dryrun))
 			return mem - base;
-- 
2.11.0