Change RPi bootargs order to keep cgroup memory controller enabled

[sairon]

With "cgroup: Use kernel command line to disable memory cgroup" merged to RPi kernel as 86099de [1], the device tree now contains "cgroup_disable=memory" parameter. The parameters are parsed in the order defined in the cmdline and with the previous order, the memory CG ends up disabled. Switching the order fixes that and makes the order similar to what we get with standard bootloader and parameters in cmdline.txt only.

The possible downside is that it won't be possible to override parameters from hardcoded bootargs_hassos using cmdline.txt anymore, however, it's unlikely any of these parameters will need to be adjusted by users.

Fixes #3765

[1] raspberrypi/linux@86099de

Summary by CodeRabbit

• Improvements
  • Updated boot script for Raspberry Pi devices to modify the order of boot arguments concatenation
  • Adjusted the sequence of bootargs variables to potentially change kernel parameter precedence
  • Changes apply to multiple Raspberry Pi board configurations (standard and Yellow models)

[coderabbitai]

📝 Walkthrough

Walkthrough

The pull request modifies the boot scripts for Raspberry Pi devices, specifically changing the order of concatenation for the bootargs environment variable. In three different boot script files (uboot-boot.ush, uboot-boot64.ush, and yellow/uboot-boot64.ush), the changes involve reordering how boot arguments are constructed. The modification switches the placement of bootargs_rpi and bootargs_hassos, placing bootargs_rpi first in the concatenation sequence. This alteration affects how boot parameters are assembled for kernel loading across different Raspberry Pi configurations.

Changes

File	Change Summary
buildroot-external/board/raspberrypi/uboot-boot.ush	Reordered bootargs concatenation, placing bootargs_rpi before bootargs_hassos
buildroot-external/board/raspberrypi/uboot-boot64.ush	Reordered bootargs concatenation, placing bootargs_rpi before bootargs_hassos
buildroot-external/board/raspberrypi/yellow/uboot-boot64.ush	Reordered bootargs concatenation, placing bootargs_rpi before bootargs_hassos

Assessment against linked issues

Objective	Addressed	Explanation
DNS Lookup Performance [#3768]	❌	Changes to boot scripts do not directly address reverse DNS lookup delays

Note: The linked issue relates to DNS performance, which is not impacted by the boot script modifications in this pull request. The changes appear to be unrelated to the reported DNS resolution problem.

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📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 29c8cf8 and 3fd3760.

📒 Files selected for processing (3)

• buildroot-external/board/raspberrypi/uboot-boot.ush (1 hunks)
• buildroot-external/board/raspberrypi/uboot-boot64.ush (1 hunks)
• buildroot-external/board/raspberrypi/yellow/uboot-boot64.ush (1 hunks)

🔇 Additional comments (6)

buildroot-external/board/raspberrypi/uboot-boot64.ush (2)

45-45: Reordering the arguments ensures the memory cgroup remains enabled.

By placing ${bootargs_rpi} first, you override any undesired cgroup_disable=memory flags. This is consistent with the PR's objective of retaining the memory cgroup controller.

---

53-53: Maintain consistent logic for slot B.

Reordering the boot args for slot B ensures uniform handling between the two boot slots, keeping the memory cgroup in effect for both.

buildroot-external/board/raspberrypi/uboot-boot.ush (2)

45-45: Consistent concatenation order improves predictability.

Reversing the order to ${bootargs_rpi} ${bootargs_hassos} ... prevents the unwanted disabling of the memory cgroup. This aligns with the standard approach to preserve cgroup configs.

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53-53: Uniform parameter order for slot B.

Applying the same ordering ensures both boot slots use the same logic, preventing discrepancies that could disable cgroups on slot B.

buildroot-external/board/raspberrypi/yellow/uboot-boot64.ush (2)

71-71: Corrected argument sequence retains cgroup memory controller.

By placing bootargs_rpi first, this prevents the kernel from applying a disable flag from the device tree.

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79-79: Slot B boot argument consistency.

Mirroring the slot A change here ensures no cgroup-related inconsistencies arise during B slot boots.

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