Ron,
On 10/26/22 17:59, [email protected] wrote:
Hi,
I'm new here and relatively new to working with Yocto (creating my own
layers anyways). I'm working on developing a SOM platform based on
Renesas RZ series of MPUs.
Welcome. When asking a question on a mailing list it is always advisable
to put all relevant information pertaining to the question into the
email and be specific about what you think the problem is. It alleviates
people from having to collect additional data to understand the problem.
I've followed the guide on Digikey by Shawn Hymel to learn about
device tree patching
(https://www.digikey.ca/en/maker/projects/intro-to-embedded-linux-part-5-how-to-enable-i2c-in-the-yocto-project/6843bbf9a83c4c96888fccada1e7aedf).
I assume many of you know about it as well.
Not necessarily. There are so many different devices and there's
probably nobody who knows them all. :)
It does a good job in describing how to add changes in a dts file. In
the example, a i2c5 node is added in the dts, overwriting what had
been defined in the original dtsi file and I'm doubting the
cleanliness of it.
It is good practice to override definitions from a dtsi in a dts. That
is the entire idea of the device tree include file which is what the 'i'
suggests. The idea is to use dtsi to define device nodes that are shared
between different platforms. Some of them are always enabled since all
platforms use them. Others, like the i2c bus in question, may only be
used on some devices and hence they are disabled. Some nodes might only
be templates and the platform's dts needs to complete them if they are used.
In this particular case it would have been better to simply add
&i2c5 {
status = "ok";
};
to the dts as the other definitions were already present as such in the
dtsi stm32mp15xx-dkx.dtsi
Would it not be better, to patch the node in the dtsi file and add the
required changes there instead of adding them to the dts file
essentially overwriting what was set previously? I imagine this will
essentially lead to two nodes being defined with the same name, the
latter just overwriting the former, is that so?
Nope, that is the idea of using the & before the device node name. All
of the &'s and the node's root definition will be merged by the device
tree compiler into the resulting device node definition. In this case
the i2c5 node's root definition is in stm32mp151.dtsi which is included
by stm32mp153.dts which is in turn included by stm32mp157.dtsi which is
included by stm32157d-dk1.dts. (I might be wrong with the details of the
chain as just browsed through it quickly but you get the idea.)
How would one go about patching the dtsi and making sure that the
patch is applied before ther file is included?
I don't recommend doing this but the example explains how to patch the
dts file. It works the same way for the dtsi.
Thank you all,
Mistyron
:rjs
--
Rudolf J Streif
CEO/CTO
1.855.442.3386
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