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[83.42.172.119]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b2ab00ff3dsm24999655e9.14.2026.11.02.13.16.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Nov 2026 13:16:42 -0800 (PST) From: Enric Balletbo i Serra Date: Mon, 02 Nov 2026 22:16:22 +0100 Subject: [PATCH v2 3/3] clocksource/drivers/nxp-stm: Increase min_delta to 20us for PREEMPT_RT 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 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261102-nxp-stm-fixes-v2-3-8ca2706f30ef@redhat.com> References: <20261102-nxp-stm-fixes-v2-0-8ca2706f30ef@redhat.com> In-Reply-To: <20261102-nxp-stm-fixes-v2-0-8ca2706f30ef@redhat.com> To: Daniel Lezcano , Thomas Gleixner , Maxime Coquelin , Alexandre Torgue , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt Cc: linux-kernel@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-rt-devel@lists.linux.dev, Ghennadi Procopciuc , NXP S32 Linux Team , stable@vger.kernel.org, Enric Balletbo i Serra X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1793654192; l=1953; i=eballetb@redhat.com; s=20261026; h=from:subject:message-id; bh=9U7e/e2EyDS47BqXM0Wq4E/IVIq+iDMzJy9Mz8G/8z0=; b=I3diUql5Q6GbqX8veSUe45rbF94jf6KgRxB2o4ixEqSLRhaEof0uU+OQxrTWrQXV/bTJ4ErDo +5AE3K8aDZ7CcqtoXD4Mb0PjXDAxuRMGD18t/k2lWRpFU20e7nZ+1KK X-Developer-Key: i=eballetb@redhat.com; a=ed25519; pk=5zh6xuAxTiQwglL2NXQFqWuyRPmCE8T5KPXLbNXhnKI= Under heavy bus contention on PREEMPT_RT kernels, a 2us min_delta is too tight and causes ~32-second timer soft lockups. Increase min_delta from 2us to 20us (~2,660 cycles at 133 MHz). This provides sufficient margin under severe bus contention to ensure the channel-enable write completes well before the counter reaches the match value, resolving the 32-second soft lockup. Fixes: cec32ac75827 ("clocksource/drivers/nxp-timer: Add the System Timer Module for the s32gx platforms") Signed-off-by: Enric Balletbo i Serra --- drivers/clocksource/timer-nxp-stm.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/drivers/clocksource/timer-nxp-stm.c b/drivers/clocksource/timer-nxp-stm.c index ed7662a4e2bc..a1a0e23d3342 100644 --- a/drivers/clocksource/timer-nxp-stm.c +++ b/drivers/clocksource/timer-nxp-stm.c @@ -335,14 +335,18 @@ static int nxp_stm_clockevent_starting_cpu(unsigned int cpu) /* * The timings measurement show reading the counter register * and writing to the comparator register takes as a maximum - * value 1100 ns at 133MHz rate frequency. The timer must be - * set above this value and to be secure we set the minimum - * value equal to 2000ns, so 2us. + * value 1100 ns at 133MHz rate frequency. However, under heavy + * bus contention on PREEMPT_RT, 2us is too tight and can allow + * the counter to pass the match value before the channel-enable + * write takes effect, leading to 32s wraparounds. * - * minimum ticks = (rate / MICRO) * 2 + * Increase to 20us to guarantee the comparator channel is fully + * enabled before the match value is reached. + * + * minimum ticks = (rate / MICRO) * 20 */ clockevents_config_and_register(&stm_timer->ced, stm_timer->rate, - (stm_timer->rate / MICRO) * 2, 0x7FFFFFFFU); + (stm_timer->rate / MICRO) * 20, 0x7FFFFFFFU); return 0; } -- 2.56.0