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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 6/10/23 10:32, Cédric Le Goater wrote:
> 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 ?

I *think* QEMU should generate DT blob with the qemu_fdt API (see
"sysemu/device_tree.h") with all the devices emulated, not forward
a Linux one.