linux-kernel - Re: [PATCH V4 0/3] scripts: dtc: Build fdtoverlay

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Date:   Wed, 3 Feb 2021 15:21:27 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Bill Mills <bill.mills@...aro.org>, anmar.oueja@...aro.org,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH V4 0/3] scripts: dtc: Build fdtoverlay

On 01-02-21, 15:07, David Gibson wrote:
> On Mon, Jan 25, 2021 at 09:42:21PM -0600, Frank Rowand wrote:
> > Before having looked at libfdt only at a cursory level while debugging the proposed
> > use of fdtoverlay in Linux, my first thought was that maybe it would be possible
> > to add warning and error messages within "#ifdef" blocks, or other ways that
> > cause the error code to _not_ be compiled as part of library version of libfdt,
> > but only be compiled as part of fdtoverlay _when built in the Linux kernel_
> > (noting that the proposed Linux patch builds the libfdt files as part of
> > the fdtoverlay compile instead of as a discrete library).  After looking at
> > the libfdt source a tiny bit more carefully, I would probably shoot down this
> > suggestion, as it makes the source code uglier and harder to understand and
> > maintain for the primary purpose of being an embedded library.
> 
> Oof.  That sounds really ugly, but maybe it could be pulled off.

I started looking at this and I was able to get to a not so ugly
solution.

Do this in dtc:
-------------------------8<-------------------------
---
 dtc.h        | 6 ++++++
 fdtoverlay.c | 2 ++
 2 files changed, 8 insertions(+)

diff --git a/dtc.h b/dtc.h
index d3e82fb8e3db..cc1e591b3f8c 100644
--- a/dtc.h
+++ b/dtc.h
@@ -29,6 +29,12 @@
 #define debug(...)
 #endif
 
+#ifdef VERBOSE
+#define pr_err(...)    fprintf(stderr, __VA_ARGS__)
+#else
+#define pr_err(...)
+#endif
+
 #define DEFAULT_FDT_VERSION    17
 
 /*
diff --git a/fdtoverlay.c b/fdtoverlay.c
index 5350af65679f..28ceac0d8079 100644
--- a/fdtoverlay.c
+++ b/fdtoverlay.c
@@ -16,6 +16,7 @@
 
 #include <libfdt.h>
 
+#include "dtc.h"
 #include "util.h"
 
 #define BUF_INCREMENT  65536
@@ -76,6 +77,7 @@ static void *apply_one(char *base, const char *overlay, size_t *buf_len,
        if (ret) {
                fprintf(stderr, "\nFailed to apply '%s': %s\n",
                        name, fdt_strerror(ret));
+               pr_err("New error\n");
                goto fail;
        }
 

-------------------------8<-------------------------
And do this in kernel:
-------------------------8<-------------------------

diff --git a/scripts/dtc/Makefile b/scripts/dtc/Makefile
index c8c21e0f2531..9dafb9773f06 100644
--- a/scripts/dtc/Makefile
+++ b/scripts/dtc/Makefile
@@ -13,6 +13,7 @@ dtc-objs      += dtc-lexer.lex.o dtc-parser.tab.o
 libfdt-objs    := fdt.o fdt_ro.o fdt_wip.o fdt_sw.o fdt_rw.o fdt_strerror.o fdt_empty_tree.o fdt_addresses.o fdt_overlay.o
 libfdt         = $(addprefix libfdt/,$(libfdt-objs))
 fdtoverlay-objs        := $(libfdt) fdtoverlay.o util.o
+HOSTCFLAGS_fdtoverlay.o := -DVERBOSE
 
 # Source files need to get at the userspace version of libfdt_env.h to compile
 HOST_EXTRACFLAGS += -I $(srctree)/$(src)/libfdt

-------------------------8<-------------------------

Will that be acceptable ? With this we can add as many error messages
to libfdt without affecting any other users of it other than Linux.

-- 
viresh