linux-kernel - [PATCH 2/2] clocksource: imx-tpm: fix next event not taking effect sometime

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Message-Id: <20240725193355.1436005-2-Frank.Li@nxp.com>
Date: Thu, 25 Jul 2024 15:33:55 -0400
From: Frank Li <Frank.Li@....com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Dong Aisheng <aisheng.dong@....com>,
	linux-kernel@...r.kernel.org (open list:CLOCKSOURCE, CLOCKEVENT DRIVERS),
	imx@...ts.linux.dev (open list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE),
	linux-arm-kernel@...ts.infradead.org (moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE)
Cc: imx@...ts.linux.dev
Subject: [PATCH 2/2] clocksource: imx-tpm: fix next event not taking effect sometime

From: Jacky Bai <ping.bai@....com>

The value written into the TPM CnV can only be updated into the hardware
when the counter increases. Additional writes to the CnV write buffer are
ignored until the register has been updated. Therefore, we need to check
if the CnV has been updated before continuing. This may require waiting for
1 counter cycle in the worst case.

Cc: <stable@...r.kernel.org>
Fixes: 059ab7b82eec ("clocksource/drivers/imx-tpm: Add imx tpm timer support")
Signed-off-by: Jacky Bai <ping.bai@....com>
Reviewed-by: Peng Fan <peng.fan@....com>
Reviewed-by: Ye Li <ye.li@....com>
Reviewed-by: Jason Liu <jason.hui.liu@....com>
Signed-off-by: Frank Li <Frank.Li@....com>
---
 drivers/clocksource/timer-imx-tpm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/clocksource/timer-imx-tpm.c b/drivers/clocksource/timer-imx-tpm.c
index cd23caf1e5999..92c025b70eb62 100644
--- a/drivers/clocksource/timer-imx-tpm.c
+++ b/drivers/clocksource/timer-imx-tpm.c
@@ -90,6 +90,14 @@ static int tpm_set_next_event(unsigned long delta,
 	writel(next, timer_base + TPM_C0V);
 	now = tpm_read_counter();
 
+	/*
+	 * Need to wait CNT increase at least 1 cycle to make sure
+	 * the C0V has been updated into HW.
+	 */
+	if ((next & 0xffffffff) != readl(timer_base + TPM_C0V))
+		while (now == tpm_read_counter())
+			;
+
 	/*
 	 * NOTE: We observed in a very small probability, the bus fabric
 	 * contention between GPU and A7 may results a few cycles delay
-- 
2.34.1