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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