Re: [PATCH 3/7] watchdog: imx7ulp_wdt: Check CMD32EN in wdog init

On Tue, Aug 23, 2022 at 05:46:55AM +0000, Alice Guo (OSS) wrote:

quoted

-----Original Message-----
From: Guenter Roeck <redacted> On Behalf Of Guenter Roeck
Sent: Monday, August 22, 2022 10:06 PM
To: Alice Guo (OSS) <redacted>
Cc: wim@linux-watchdog.org; shawnguo@kernel.org;
s.hauer@pengutronix.de; festevam@gmail.com; kernel@pengutronix.de;
dl-linux-imx [off-list ref]; linux-watchdog@vger.kernel.org;
linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/7] watchdog: imx7ulp_wdt: Check CMD32EN in wdog
init

On Tue, Aug 16, 2022 at 12:36:39PM +0800, Alice Guo (OSS) wrote:

quoted

From: Ye Li <redacted>

When bootloader has enabled the CMD32EN bit, switch to use 32bits
unlock command to unlock the CS register. Using 32bits command will
help on avoiding 16 bus cycle window violation for two 16 bits
commands.

Signed-off-by: Ye Li <redacted>
Signed-off-by: Alice Guo <redacted>
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
Acked-by: Jason Liu <redacted>
---
 drivers/watchdog/imx7ulp_wdt.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/watchdog/imx7ulp_wdt.c

b/drivers/watchdog/imx7ulp_wdt.c index b8ac0cb04d2f..a0f6b8cea78f
100644

--- a/drivers/watchdog/imx7ulp_wdt.c
+++ b/drivers/watchdog/imx7ulp_wdt.c

@@ -180,11 +180,16 @@ static int imx7ulp_wdt_init(void __iomem *base,

unsigned int timeout)

 	local_irq_disable();

-	mb();
-	/* unlock the wdog for reconfiguration */
-	writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
-	writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
-	mb();
+	val = readl(base + WDOG_CS);
+	if (val & WDOG_CS_CMD32EN) {
+		writel(UNLOCK, base + WDOG_CNT);
+	} else {
+		mb();
+		/* unlock the wdog for reconfiguration */
+		writel_relaxed(UNLOCK_SEQ0, base + WDOG_CNT);
+		writel_relaxed(UNLOCK_SEQ1, base + WDOG_CNT);
+		mb();

Now this is intermixing writel() with writel_relaxed(), making the code all but
impossible to understand.

Guenter

Hi Guenter,

Intermixing writel() with writel_relaxed() is unavoidable here. Because there cannot be a memory barrier between writing UNLOCK_SEQ0 and writing UNLOCK_SEQ1. This may be determined by hardware design.

If it is indeed impossible to configure the watchdog for 32-bit
access mode, that needs to be explained in the code and backed up,
for example with a reference to the documentation. Similar,
it needs to be documented in the code why writel() does not work
here and why mb() is needed.

Thanks,
Guenter

Best Regards,
Alice Guo
 

quoted

quoted

+	}

 	ret = imx7ulp_wdt_wait(base, WDOG_CS_ULK);
 	if (ret)
--
2.17.1

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