Re: [PATCH v2] pc-bios/meson.build: Silent unuseful DTC warnings

["Cédric Le Goater" <clegoate@redhat.com>]

On 10/6/23 10:18, Philippe Mathieu-Daudé wrote:
> On 6/10/23 10:13, Cédric Le Goater wrote:
>> On 10/6/23 08:47, Philippe Mathieu-Daudé wrote:
>>> QEMU consumes some device tree blobs, so these have been committed
>>> to the tree in as firmware, along with the device tree source used
>>> to generate them. We know the blobs are "good enough" to have QEMU
>>> boot a system, so we don't really maintain and rebuild the sources.
>>>
>>> These blobs were generated with older 'dtc' binaries. We use the
>>> v1.6.1 version since 2021 (commit 962fde57b7 "dtc: Update to version
>>> 1.6.1").
>>>
>>> Since commit 6e0dc9d2a8 ("meson: compile bundled device trees"),
>>> if dtc binary is available, it is directly used to compile the
>>> device tree sources. New versions of 'dtc' add checks which display
>>> warnings or errors. Our sources are a bit old, so dtc v1.6.1 now
>>> emit the following warnings on a fresh build:
>>>
>>>    [163/3414] Generating pc-bios/canyonlands.dts with a custom command
>>>    pc-bios/canyonlands.dts:47.9-50.4: Warning (unit_address_vs_reg): /memory: node has a reg or ranges property, but no unit name
> ...
> 
>>>  From QEMU perspective, these warnings are not really useful. It is
>>> the responsibility of developers adding DT source/blob to QEMU
>>> repository to check the source doesn't produce warnings, but as
>>> long as the blob is useful enough, QEMU can consume it. So these
>>> warnings don't add any value, instead they are noisy and might
>>> distract us to focus on important warnings. Better disable them.
>>>
>>> 'dtc' provides the '--quiet' option for that:
>>>
>>>    $ dtc --help
>>>    Usage: dtc [options] <input file>
>>>
>>>    Options: -[qI:O:o:V:d:R:S:p:a:fb:i:H:sW:E:@AThv]
>>>      -q, --quiet
>>>            Quiet: -q suppress warnings, -qq errors, -qqq all
>>>
>>> Update meson to disable these unuseful DTC warnings.
>>
>>
>> Why not try fixing the .dts instead ? These still exist under Linux :
>>
>>    ./arch/powerpc/boot/dts/canyonlands.dts
>>    ./arch/powerpc/boot/dts/bamboo.dts
> 
> Because QEMU != Linux, and there isn't always overlap between
> communities?

sure but bamboo.dts came from Linux. So this should be safe to update.
Alex Graf did 10 years ago.

I can not tell for the sam460ex. It is probably safer to keep it as it is.

Sweeping dtc warnings under the rug for all .dts doesn't seem a good idea.
Should we get rid of the .dts and only keep the .dtb then ?

Thanks,

C.

> 1/ I tried but there isn't much interest:
> https://lore.kernel.org/qemu-devel/20230914204206.79351-1-philmd@linaro.org/
> 
> 2/ Peter and Zoltan raised issue with old firmwares when changing
> properties such 'stdout-path', see this thread:
> https://lore.kernel.org/qemu-devel/CAFEAcA-WJ9J1YQunJ+bSG=wnpxh1By+Bf18j2CyV7G0vZ=8b7g@mail.gmail.com/