英文:
When should we use device tree overlay over multiple device tree blob?
问题
你是否应该创建多个dtsi文件以适应每种配置，然后编译多个dtb文件并将其安装在/boot/中，还是应该使用设备树叠加？
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如果你想继续使用现有的方法，为每种硬件配置创建多个独立的dts文件，然后编译并安装对应的dtb文件，这是一种有效的方式。这样，每种配置都有一个单独的dtb文件，可以在启动时选择正确的dtb。
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另一方面，使用设备树叠加也是一种可行的方法。你可以保持一个基本的dts文件，然后为每种配置创建叠加（overlay）文件，每个叠加文件仅包含与特定配置相关的更改。在运行时，可以加载适当的叠加文件以覆盖基本的设备树信息，从而适应不同的硬件配置。
选择哪种方法取决于你的需求和偏好。使用叠加文件可以使设备树更加模块化，但也需要在运行时加载叠加，而不是在编译时生成不同的dtb文件。根据你的具体情况和偏好，选择合适的方法。
英文:
I have a custom board based on iMX8MP processors. This board can have 3 different hardware configuration. Basically the number of adc and shift registers are different between them. I want to be able to select correct dtb at boot time based on a truth table. I have done a u-boot script to select correct dtb which should be located in /boot/.
For a time being, I have generated all dtbs with dtc command. Then I generated dts again from those dtbs to get rid of all dtsi and to have one compact dts file for each hardware configuration.
My yocto recipe look like this:
SUMMARY = "U-boot script: auto select dtb for devboard"
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""
COMPATIBLE_MACHINE = "devboard"
DEPENDS = "u-boot-mkimage-native dtc-native"
SRC_URI = "file://autoselect-dtb.txt \
file://devboard-cirrus8.dts \
file://devboard-cirrus16.dts \
file://devboard-cirrus32.dts"
do_compile() {
mkimage -A arm64 -O linux -T script -C none -d "${WORKDIR}/autoselect-dtb.txt" boot.scr
dtc -I dts -O dtb -o devboard-cirrus8.dtb ${WORKDIR}/devboard-cirrus8.dts
dtc -I dts -O dtb -o devboard-cirrus16.dtb ${WORKDIR}/devboard-cirrus16.dts
dtc -I dts -O dtb -o devboard-cirrus32.dtb ${WORKDIR}/devboard-cirrus32.dts
}
do_install() {
install -d ${D}/boot/
install -m 0644 boot.scr ${D}/boot/
install -m 0644 devboard-cirrus8.dtb ${D}/boot/
install -m 0644 devboard-cirrus16.dtb ${D}/boot/
install -m 0644 devboard-cirrus32.dtb ${D}/boot/
}
FILES:${PN} = "/boot/*"
I am aware that this is not good practice. Now I am confused, should I create multiple dtsi to suit each configuration then compile multiple dtb then install it in /boot/ or should I use device tree overlay ?
答案1
得分: 3
这取决于使用情况。DTSI用于开发人员，而DTO用于最终用户。
因此，如果您正在为某些客户开发一个“平台”，比如树莓派(RPi)，或者在某些情况下，某人需要非常频繁地更改功能（集成商、服务人员），您应该优先选择DTO，让最终用户决定他们需要哪些节点。
对于您作为开发者，或者在您的DTB已经是最终版本的情况下（例如，一些设备已经从工厂发布，不再打算重新配置），我建议使用DTSI，带有定义。
如果您想在启动时选择要加载的DTB，我认为这完全取决于您 - 是使用基本DTB的DTO，还是不使用DTO的不同DTB。
注意：
为了避免编译和反编译循环，您可以使用cpp（C预处理器）来摆脱所有类似于DTSI的内容：
CPP_FLAGS := -nostdinc -I $(INCLUDE) -undef -x assembler-with-cpp
$(TARGET_PP): $(TARGET_DTS)
cpp $(CPP_FLAGS) $(TARGET_DTS) $(TARGET_PP)
然后，您将获得$(TARGET_PP)文件，其中包含您的整个DTS及所有包含的内容（但仍然不包括未分组的节点）。
英文:
It depends on use case. DTSI's are for developers while DTO's are for end-users.
So if you are working on a "platform" for some customers, like RPi or cases when someone needs to change functionality (integrators, service staff) very frequently - you should prefer DTO's to let end-users decide what nodes they need.
For you as for developer, or in case your DTB is final (for example - some device which is released form factory and not intended to be reconfigured anymore) I would suggest use DTSI's, with defines.
If you want to select DTB to load at boot time, I think it's all up to you - to use DTO's with base DTB or to use different DTB's w/o DTO's.
NB
To omit compiling-decompiling cycle you can use cpp (C Preprocessor) to get rid of all DTSI's like that:
CPP_FLAGS := -nostdinc -I $(INCLUDE) -undef -x assembler-with-cpp
$(TARGET_PP): $(TARGET_DTS)
cpp $(CPP_FLAGS) $(TARGET_DTS) $(TARGET_PP)
and you'll get $(TARGET_PP) file which will contain your whole DTS with all includes (but still with not grouped nodes).
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