Re: [PATCH] of: build dbts with symbols when CONFIG_OF_OVERLAY is set

From: Andre Heider
Date: Wed Dec 20 2017 - 03:08:17 EST

On 18/12/17 23:10, Frank Rowand wrote:
On 12/16/17 09:25, Andre Heider wrote:
Hi Frank,

On 15/12/17 22:06, Frank Rowand wrote:
On 12/14/17 07:12, Andre Heider wrote:
The overlay feature requires the base dtb to be built with symbols, so
lets build the dtbs with symbols when overlay support was explicitly

With CONFIG_OF_ALL_DTBS on ARCH=arm the 989 dtb files grow about ~38% on

Totals in bytes with the 3 biggest ones:

ÂÂÂÂ90471ÂÂÂ arch/arm/boot/dts/am57xx-beagle-x15-revc.dtb
ÂÂÂÂ90521ÂÂÂ arch/arm/boot/dts/am57xx-beagle-x15-revb1.dtb
ÂÂÂÂ92639ÂÂÂ arch/arm/boot/dts/dra7-evm.dtb
ÂÂÂÂ25731296ÂÂÂ total

ÂÂÂÂ133203ÂÂÂ arch/arm/boot/dts/am57xx-beagle-x15-revc.dtb
ÂÂÂÂ133237ÂÂÂ arch/arm/boot/dts/am57xx-beagle-x15-revb1.dtb
ÂÂÂÂ134545ÂÂÂ arch/arm/boot/dts/dra7-evm.dtb
ÂÂÂÂ35464440ÂÂÂ total

Signed-off-by: Andre Heider <a.heider@xxxxxxxxx>


while playing around with overlays I noticed that I needed to rebuilt
my distro's device trees because they didn't come with symbols.

Is that for a reason, maybe the not so minor increase in size?

Yes, size is the issue.


 drivers/of/unittest-data/Makefile | 7 -------
 scripts/Makefile.lib | 5 +++++
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/of/unittest-data/Makefile b/drivers/of/unittest-data/Makefile
index 32389acfa616..b65061013512 100644
--- a/drivers/of/unittest-data/Makefile
+++ b/drivers/of/unittest-data/Makefile
@@ -15,13 +15,6 @@ targets += overlay.dtb overlay.dtb.S
 targets += overlay_bad_phandle.dtb overlay_bad_phandle.dtb.S
 targets += overlay_bad_symbol.dtb overlay_bad_symbol.dtb.S
 targets += overlay_base.dtb overlay_base.dtb.S
-# enable creation of __symbols__ node
-DTC_FLAGS_overlay := -@
-DTC_FLAGS_overlay_bad_phandle := -@
-DTC_FLAGS_overlay_bad_symbol := -@
-DTC_FLAGS_overlay_base := -@

No. The unittests require these to be set unconditionally.

diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 1ca4dcd2d500..c7ba4aa8a07a 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -278,6 +278,11 @@ DTC_FLAGS += -Wnode_name_chars_strict \
ÂÂÂÂÂ -Wproperty_name_chars_strict
 +ifeq ($(CONFIG_OF_OVERLAY),y)
+# enable creation of __symbols__ node
+DTC_FLAGS += -@
 DTC_FLAGS += $(DTC_FLAGS_$(basetarget))
  # Generate an assembly file to wrap the output of the device tree compiler

Not needed. Instead set DTC_FLAGS in the make command. For example:

ÂÂÂ DTC_FLAGS=-@ make qcom-apq8074-dragonboard.dtb

There are a few architecture Makefiles that need to be fixed to not unconditionally

Rebuilding the dts files manually with symbols isn't the problem. The
idea was to enable it with a switch which distros simply can flip.

Passing DTC_FLAGS to `make` would work too I guess, but on multi
platform builds that's still the same issue if there're boards which
can't handle that because of the size increase.

Would a solution which enables symbols per family work? E.g.
CONFIG_MACH_SUN7I chooses to use -@ because it can handle it.


Making it easy for distros to increase the size of .dtb files is
not the correct answer. We are trying to decrease the footprint
of devicetree, not increase it.

I'm not sure I follow. If it's not acceptable to increase the size, why's there overlay support in the first place?

There're distros/downstreams that support overlays today, like armbian, beaglebone and rpi. All carrying their own patches to enable symbols [1] [2] [3] and I'm sure others will follow. Why can't there be some sort of switch for those to build their dtbs with symbols?