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Date: Mon, 20 Oct 2025 11:17:04 -0300
From: Hiago De Franco <hiagofranco@...il.com>
To: Beleswar Padhi <b-padhi@...com>
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	regressions@...ts.linux.dev
Subject: [REGRESSION] Suspend to RAM does not work anymore with
 k3-am62-ti-ipc-firmware.dtsi

Hello all,

After commit 1d6161617c10 (“arm64: dts: ti: k3-am62-ti-ipc-firmware:
Refactor IPC cfg into new dtsi”), suspend-to-RAM stopped working on
AM62x.

When I originally tested that change, I did not test suspend-to-RAM
functionality, but our testing infrastructure caught this regression.

See the log below:

root@...din-am62-15479173:~# cat /sys/class/remoteproc/remoteproc*/state
offline
offline
offline
root@...din-am62-15479173:~# echo mem > /sys/power/state
[   37.798686] PM: suspend entry (deep)
[   37.805942] Filesystems sync: 0.003 seconds
[   37.811965] Freezing user space processes
[   37.819214] Freezing user space processes completed (elapsed 0.002 seconds)
[   37.826469] OOM killer disabled.
[   37.829721] Freezing remaining freezable tasks
[   37.835557] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
[   37.843057] printk: Suspending console(s) (use no_console_suspend to debug)
[   37.953874] omap-mailbox 29000000.mailbox: fifo 5 has unexpected unread messages
[   37.953909] omap-mailbox 29000000.mailbox: PM: dpm_run_callback(): platform_pm_suspend returns -16
[   37.953941] omap-mailbox 29000000.mailbox: PM: failed to suspend: error -16
[   37.953967] PM: Some devices failed to suspend, or early wake event detected
[   37.973876] am65-cpsw-nuss 8000000.ethernet: set new flow-id-base 19
[   37.984655] am65-cpsw-nuss 8000000.ethernet end0: PHY [8000f00.mdio:00] driver [TI DP83867] (irq=353)
[   37.985655] am65-cpsw-nuss 8000000.ethernet end0: configuring for phy/rgmii-rxid link mode
[   38.009002] usb-conn-gpio connector: repeated role: device
[   38.013377] lt8912 1-0048: PM: dpm_run_callback(): lt8912_bridge_resume [lontium_lt8912b] returns -121
[   38.013420] lt8912 1-0048: PM: failed to resume async: error -121
[   38.153252] OOM killer enabled.
[   38.156422] Restarting tasks: Starting
[   38.163532] Restarting tasks: Done
[   38.167252] random: crng reseeded on system resumption
[   38.173031] PM: suspend exit

The omap-mailbox driver returns -EBUSY because it detects an unexpected
unread message on FIFO 5.  As I understand it, this FIFO corresponds to
the communication channel between the DM R5 and the Cortex-M4 cores.

DM R5 sends a message that is never consumed, since no firmware is
running on the M4 (the core is offline). This unhandled message prevents
the system from entering suspend.

This issue also appears on the downstream TI kernel, which I reported
earlier [1] (for reference).

The following patch resolves the problem:

diff --git a/arch/arm64/boot/dts/ti/k3-am62-ti-ipc-firmware.dtsi b/arch/arm64/boot/dts/ti/k3-am62-ti-ipc-firmware.dtsi
index ea69fab9b52b..e07cf3290cc3 100644
--- a/arch/arm64/boot/dts/ti/k3-am62-ti-ipc-firmware.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-am62-ti-ipc-firmware.dtsi
@@ -26,11 +26,6 @@ mbox_m4_0: mbox-m4-0 {
                ti,mbox-rx = <0 0 0>;
                ti,mbox-tx = <1 0 0>;
        };
-
-       mbox_r5_0: mbox-r5-0 {
-               ti,mbox-rx = <2 0 0>;
-               ti,mbox-tx = <3 0 0>;
-       };
 };

 &mcu_m4fss {
@@ -45,7 +40,6 @@ &wkup_r5fss0 {
 };

 &wkup_r5fss0_core0 {
-       mboxes = <&mailbox0_cluster0 &mbox_r5_0>;
        memory-region = <&wkup_r5fss0_core0_dma_memory_region>,
                        <&wkup_r5fss0_core0_memory_region>;
        status = "okay";

Ultimately  this issue is related to the omap driver itself:

1. We should have a functionatlly to save and restore the messages into
the mailbox, instead of preveting it to go into suspend.

2. Or we could not check all 16 FIFOs if the kernel does not own them:

	for (fifo = 0; fifo < mdev->num_fifos; fifo++) {
		if (mbox_read_reg(mdev, MAILBOX_MSGSTATUS(fifo))) {
			dev_err(mdev->dev, "fifo %d has unexpected unread messages\n",
				fifo);
			return -EBUSY;
		}
	}

Setting the number of FIFOs to 4 in the device tree also resolves this
issue.

Do you have suggestions on how best to fix this in the driver, or should
we consider reverting the DTS change until suspend-to-RAM works again?

#regzbot introduced: 1d6161617c

[1] https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1557295/am62p-mailbox-channel-is-not-freed-during-r5-remoteproc-stop-call/6069413

Best regards,
Hiago.

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