Hi Frank,

On Wed, Sep 5, 2018 at 10:54 PM Frank Rowand [off-list ref] wrote:

On 09/04/18 01:27, Tero Kristo wrote:

quoted

Add support for TI specific DT subdir, along with support for building
DT overlays. Right now, no DT files are specified in this directory,
those are to be added later.

Signed-off-by: Tero Kristo <redacted>

quoted

--- /dev/null
+++ b/arch/arm/boot/dts/ti/Makefile

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Make file to build device tree binaries for boards based on
+# Texas Instruments Inc processors
+#
+# Copyright (C) 2016-2018 Texas Instruments Incorporated - http://www.ti.com/
+#
+
+DTC_FLAGS += -@

I will nack any attempt to unconditionally compile a devicetree file with the
-@ flag (which adds symbols to the resulting .dtb).  The resulting overhead
is not acceptable.

Adding the symbols must be under the control of the person either creating
or using the .dtb.  The way to provide that control is the challenging part.

One way would be to configure the compile option via kbuild configuration.
There is opposition to this approach because it makes the .dtb dependent
on the Linux kernel configuration.  So suggestions of an alternative
mechanism would be welcome.

IMHO that would be quite a "soft" dependency: it's just about adding symbols
or not. No real dependency on Linux or kernel features.

Another _possible_ solution would be to add a dtc_strip tool to the dtc
project.  dtc_strip would remove the symbol information from a .dtb,
in a manner that is analogous to strip removing debug information from
a program file.

Removing unwanted symbols is indeed easier than adding them to an
existing DTB.

One aspect of unconditionally building a .dtb with symbols, then
optionally removing the symbols with dtc_strip is that it seems
like a backwards process.  For example, we don't build the kernel
with debug symbols then strip the symbols out when we don't want
them.  I'll have to mull this over if the dtc_strip method sounds
like a good approach to other people.

That's not a fair comparison: DTB symbols are not debug information,
but an ABI. It's more akin to exporting kernel symbols to (possible
out-of-tree) kernel modules, which is controlled by CONFIG_MODULES.

So a Kconfig symbol to enable it, and a dtc_strip for removing them,
makes most sense to me.

BTW, we do run strip on vmlinux ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds