From: David Gibson <david@gibson.dropbear.id.au>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Frank Rowand <frowand.list@gmail.com>,
Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
Rob Herring <robh+dt@kernel.org>,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kbuild@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
Bill Mills <bill.mills@linaro.org>,
anmar.oueja@linaro.org, Masahiro Yamada <masahiroy@kernel.org>
Subject: Re: [PATCH V4 0/3] scripts: dtc: Build fdtoverlay
Date: Fri, 22 Jan 2021 17:34:55 +1100 [thread overview]
Message-ID: <20210122063455.GE4400@yekko.fritz.box> (raw)
In-Reply-To: <20210120051740.yph4v7zldvs7szdz@vireshk-i7>
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On Wed, Jan 20, 2021 at 10:47:40AM +0530, Viresh Kumar wrote:
> +David.
>
> On 19-01-21, 11:12, Frank Rowand wrote:
> > On 1/12/21 2:28 AM, Viresh Kumar wrote:
> > > We will start building overlays for platforms soon in the kernel and
> > > would need fdtoverlay tool going forward. Lets start fetching and
> > > building it.
> > >
> > > While at it, also remove fdtdump.c file, which isn't used by the kernel.
> > >
> > > V4:
> > > - Don't fetch and build fdtdump.c
> > > - Remove fdtdump.c
> > >
> > > Viresh Kumar (3):
> > > scripts: dtc: Add fdtoverlay.c to DTC_SOURCE
> > > scripts: dtc: Build fdtoverlay tool
> > > scripts: dtc: Remove the unused fdtdump.c file
> > >
> > > scripts/dtc/Makefile | 6 +-
> > > scripts/dtc/fdtdump.c | 163 -------------------------------
> > > scripts/dtc/update-dtc-source.sh | 6 +-
> > > 3 files changed, 8 insertions(+), 167 deletions(-)
> > > delete mode 100644 scripts/dtc/fdtdump.c
> > >
> >
> > My first inclination was to accept fdtoverlay, as is, from the upstream
> > project.
> >
> > But my experiences debugging use of fdtoverlay against the existing
> > unittest overlay files has me very wary of accepting fdtoverlay in
> > it's current form.
> >
> > As an exmple, adding an overlay that fails to reply results in the
> > following build messages:
> >
> > linux--5.11-rc> make zImage
> > make[1]: Entering directory '/local/frowand_nobackup/src/git_linus/build/dragon_linus_5.11-rc'
> > GEN Makefile
> > CALL /local/frowand_nobackup/src/git_linus/linux--5.11-rc/scripts/checksyscalls.sh
> > CALL /local/frowand_nobackup/src/git_linus/linux--5.11-rc/scripts/atomic/check-atomics.sh
> > CHK include/generated/compile.h
> > FDTOVERLAY drivers/of/unittest-data/static_test.dtb
> >
> > Failed to apply 'drivers/of/unittest-data/overlay.dtb': FDT_ERR_NOTFOUND
> > make[4]: *** [/local/frowand_nobackup/src/git_linus/linux--5.11-rc/drivers/of/unittest-data/Makefile:96: drivers/of/unittest-data/static_test.dtb] Error 1
> > make[3]: *** [/local/frowand_nobackup/src/git_linus/linux--5.11-rc/scripts/Makefile.build:496: drivers/of/unittest-data] Error 2
> > make[2]: *** [/local/frowand_nobackup/src/git_linus/linux--5.11-rc/scripts/Makefile.build:496: drivers/of] Error 2
> > make[1]: *** [/local/frowand_nobackup/src/git_linus/linux--5.11-rc/Makefile:1805: drivers] Error 2
> > make[1]: Leaving directory '/local/frowand_nobackup/src/git_linus/build/dragon_linus_5.11-rc'
> > make: *** [Makefile:185: __sub-make] Error 2
> >
> >
> > The specific error message (copied from above) is:
> >
> > Failed to apply 'drivers/of/unittest-data/overlay.dtb': FDT_ERR_NOTFOUND
> >
> > which is cryptic and does not even point to the location in the overlay that
> > is problematic. If you look at the source of fdtoverlay / libfdt, you will
> > find that FDT_ERR_NOTFOUND may be generated in one of many places.
> >
> > I do _not_ want to do a full review of fdtoverlay, but I think that it is
> > reasonable to request enhancing fdtoverlay in the parent project to generate
> > usable error messages before enabling fdtoverlay in the Linux kernel tree.
That's... actually much harder than it sounds. fdtoverlay is
basically a trivial wrapper around the fdt_overlay_apply() function in
libfdt. Matching the conventions of the rest of the library, really
it's only way to report errors is a single error code.
Returning richer errors is not an easy problem in a C library,
especially one designed to be usable in embedded systems, without an
allocator or much else available.
Of course it would be possible to write a friendly command line tool
specifically for applying overlays, which could give better errors.
fdtoverlay as it stands isn't really that - it was pretty much written
just to invoke fdt_overlay_apply() in testcases.
> > fdtoverlay in it's current form adds a potential maintenance burden to me
> > (as the overlay maintainer). I now have the experience of how difficult it
> > was to debug the use of fdtoverlay in the context of the proposed patch to
> > use it with the devicetree unittest overlay .dtb files.
> >
> > -Frank
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2021-01-22 6:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-12 8:28 [PATCH V4 0/3] scripts: dtc: Build fdtoverlay Viresh Kumar
2021-01-12 8:29 ` [PATCH V4 1/3] scripts: dtc: Add fdtoverlay.c to DTC_SOURCE Viresh Kumar
2021-01-19 16:32 ` Frank Rowand
2021-01-12 8:29 ` [PATCH V4 2/3] scripts: dtc: Build fdtoverlay tool Viresh Kumar
2021-01-19 16:37 ` Frank Rowand
2021-01-20 15:47 ` Rob Herring
2021-01-12 8:29 ` [PATCH V4 3/3] scripts: dtc: Remove the unused fdtdump.c file Viresh Kumar
2021-01-19 17:12 ` [PATCH V4 0/3] scripts: dtc: Build fdtoverlay Frank Rowand
2021-01-20 5:17 ` Viresh Kumar
2021-01-22 6:34 ` David Gibson [this message]
2021-01-26 3:42 ` Frank Rowand
2021-02-01 4:07 ` David Gibson
2021-02-03 9:51 ` Viresh Kumar
2021-02-04 14:25 ` Rob Herring
2021-02-22 6:17 ` David Gibson
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