Re: [PATCH 2/2] ARM: l2c: honour status = "disabled" on the L2 cache node

[Arnd Bergmann]

On Wed, Nov 11, 2026, at 14:39, Agustin Santiago Isasmendi wrote:
> l2x0_of_init() looks the L2 cache node up by compatible and enables the
> cache whatever its status property says, so a device tree cannot keep
> the L2 cache off.
>
> On the ZTE ZX279128S (dual Cortex-A9, L2C-310 r3p3) a PCIe read on one
> CPU deadlocks against an L2C-310 line operation by physical address or a
> Cache Sync on the other CPU, and the board hangs within seconds of WiFi
> traffic.  Running with the L2 cache off avoids the deadlock, so a board
> needs a way to say so.
>
> Honour the status property, as the newer cache controller drivers
> already do (drivers/cache/ax45mp_cache.c, starfive_starlink_cache.c).
> If the firmware left the cache enabled, it cannot simply be ignored,
> since nothing would maintain it: clean, invalidate and disable it
> instead.  No in-tree L2 cache node is disabled, so nothing changes for
> existing device trees.
>
> Tested on the ZTE ZXHN H3600: with the node disabled the cache stays
> off and the system runs normally; with it enabled the cache comes up as
> before.  The firmware-enabled path was exercised with a test-only
> change that enables the cache before the check.
>
> Assisted-by: LLM
> Signed-off-by: Agustin Santiago Isasmendi <isasmendi.agus@xxxxxxxxx>

Hi Augustin,

It is a little strange to use the MMIO registers of a status="disabled"
device to turn it off, and it would be nice if we could require
the firmware to leave it in a consistent state instead, but I assume
you can't do that for the one device you are interested in because
you don't have the firmware sources, right?

In this case

Reviewed-by: Arnd Bergmann <arnd@xxxxxxxx>

but maybe add a code comment that explains this to the reader.