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Wed, 11 Nov 2026 08:56:55 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-ThreadId: Arg9H_lZnKn7 Date: Wed, 11 Nov 2026 14:56:34 +0100 From: "Arnd Bergmann" To: "Agustin Santiago Isasmendi" , "Russell King" Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, =?UTF-8?Q?Stefan_D=C3=B6singer?= , "Navid Ghahremani" , "Krzysztof Kozlowski" Message-Id: <49846243-34ae-4643-9b39-1537947fbd96@app.fastmail.com> In-Reply-To: <20261111133930.3665251-3-isasmendi.agus@gmail.com> References: <20261111133930.3665251-1-isasmendi.agus@gmail.com> <20261111133930.3665251-3-isasmendi.agus@gmail.com> Subject: Re: [PATCH 2/2] ARM: l2c: honour status = "disabled" on the L2 cache node Content-Type: text/plain Content-Transfer-Encoding: 7bit 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 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 but maybe add a code comment that explains this to the reader.