/jetson-customize-clocks

Disabling EMC DVFS via the BPMP DTB

Reference material for ../SKILL.md the "Content edit: EMC DVFS disable / enable" step.

This doc covers which nodes / properties to edit for the EMC DVFS gate. The decompile / recompile / commit mechanics live in the canonical ../../../references/bsp-customization-bpmp-dtb.md; apply the snippets below inside the protocol's "Edit the DTS" step.

Disabling EMC DVFS pins EMC at the BPMP-init rate (no scaling with bandwidth demand). It is not a single edit — bwmgr alone leaves EMC scaling on via the surviving cactmon path (and the OSP / QoS path on T26x). All required edits must land in the same BPMP DTB or the result is undefined.

SoC detection (run first)

Decompile the resolved BPMP DTB and check for the osp-controller node:

dtc -I dtb -O dts <bpmp-dtb> | grep -c osp-controller

Edits

#1 — bwmgr.enabled = <0x00> (all SoCs, mandatory)

Disables bandwidth-driven scaling requests.

bwmgr {
    enabled = <0x00>;   /* 0x01 = scale (default); 0x00 = pin at init rate */
    ...
};

#2 — cactmon.enabled = <0x00> (all SoCs, mandatory)

The EMC activity monitor that drives DVFS hints. Leaving it active while bwmgr is off lets the monitor keep firing on a frozen frequency target, producing spurious actmon events / latency anomalies.

cactmon {
    enabled = <0x00>;
    ...
};

#3 — Remove the osp-controller node (T26x mandatory, T23x skip)

The OSP (operating-state / power) controller arbitrates EMC frequency floors based on QoS clients. With bwmgr off it has nothing valid to act on; leaving the node in place can re-introduce frequency changes from the QoS path.

T23x (Orin) BPMP DTBs do not contain this node — skip on T23x.

Delete the node entirely (do NOT use status = "disabled" — OSP isn't a standard kernel-DT consumer; the node must not exist for BPMP to skip the path):

/delete-node/ osp-controller;

Equivalent inline form when editing inside the parent node: replace the osp-controller { … }; block with /delete-node/ osp-controller; at the same scope.

Re-enabling EMC DVFS

Reverse the edits that were applied:

• bwmgr.enabled = <0x01>
• cactmon.enabled = <0x01>
• (T26x only) restore the osp-controller node from the pristine BPMP DTS.

Capture the pristine osp-controller block before the first disable, or recover it later by dtc-decompiling the pristine bpmp-fw-dtb from <bsp_image.root_path>.

Why all of this is gated together

Both surviving paths are independent enough of bwmgr to keep operating against a target the firmware has already pinned. Disabling them is the only way to actually pin the EMC frequency.