linux-kernel - [PATCH v2 2/7] watchdog: imx7ulp: Add explict memory barrier for unlock sequence

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Date:   Thu, 25 Aug 2022 16:32:51 +0800
From:   "Alice Guo (OSS)" <alice.guo@....nxp.com>
To:     m.felsch@...gutronix.de, linux@...ck-us.net,
        wim@...ux-watchdog.org, shawnguo@...nel.org,
        s.hauer@...gutronix.de, festevam@...il.com
Cc:     kernel@...gutronix.de, linux-imx@....com,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/7] watchdog: imx7ulp: Add explict memory barrier for unlock sequence

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

When reconfiguring the WDOG Timer of i.MX7ULP, there is a certain
probability causes it to reset. The reason is that the CMD32EN of the
WDOG Timer of i.MX7ULP is disabled in bootloader. The unlock sequence
are two 16-bit writes to the CNT register within 16 bus clocks. Adding
mb() is to guarantee that two 16-bit writes are finished within 16 bus
clocks. Memory barriers cannot be added between these two 16-bit writes
so that writel_relaxed is used.

Suggested-by: Ye Li <ye.li@....com>
Signed-off-by: Jacky Bai <ping.bai@....com>
Signed-off-by: Alice Guo <alice.guo@....com>
Reviewed-by: Ye Li <ye.li@....com>
---

Changes for v2:
 - add the reason why memory barriers are added for unlock sequence in commit log

 drivers/watchdog/imx7ulp_wdt.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/watchdog/imx7ulp_wdt.c b/drivers/watchdog/imx7ulp_wdt.c
index 014f497ea0dc..b8ac0cb04d2f 100644
--- a/drivers/watchdog/imx7ulp_wdt.c
+++ b/drivers/watchdog/imx7ulp_wdt.c
@@ -179,9 +179,13 @@ static int imx7ulp_wdt_init(void __iomem *base, unsigned int timeout)
 	int ret;
 
 	local_irq_disable();
+
+	mb();
 	/* unlock the wdog for reconfiguration */
 	writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
 	writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
+	mb();
+
 	ret = imx7ulp_wdt_wait(base, WDOG_CS_ULK);
 	if (ret)
 		goto init_out;
-- 
2.17.1