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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Mon, 25 Sep 2023 09:20:05 +0200
Subject: [PATCH] watchdog: ixp4xx: Make sure restart always works
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Message-Id: <20230925-ixp4xx-wdt-restart-v1-1-fe2b9b131dbf@linaro.org>
To:     Wim Van Sebroeck <wim@linux-watchdog.org>,
        Guenter Roeck <linux@roeck-us.net>
Cc:     linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linus Walleij <linus.walleij@linaro.org>
Precedence: bulk

The IXP4xx watchdog in early "A0" silicon is unreliable and
cannot be registered, however for some systems such as the
USRobotics USR8200 the watchdog is the only restart option,
so implement a "dummy" watchdog that can only support restart
in this case.

Fixes: 1aea522809e6 ("watchdog: ixp4xx: Implement restart")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Other solutions like implementing a pure restart notifier
callback catch in the driver is possible, but this method
will minimize the amount of code and reuse infrastructure
in the core.
---
 drivers/watchdog/ixp4xx_wdt.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/ixp4xx_wdt.c b/drivers/watchdog/ixp4xx_wdt.c
index 607ce4b8df57..c0bf03125ec8 100644
--- a/drivers/watchdog/ixp4xx_wdt.c
+++ b/drivers/watchdog/ixp4xx_wdt.c
@@ -105,6 +105,25 @@ static const struct watchdog_ops ixp4xx_wdt_ops = {
 	.owner = THIS_MODULE,
 };
 
+/*
+ * The A0 version of the IXP422 had a bug in the watchdog making
+ * is useless, but we still need to use it to restart the system
+ * as it is the only way, so in this special case we register a
+ * "dummy" watchdog that doesn't really work, but will support
+ * the restart operation.
+ */
+static int ixp4xx_wdt_dummy(struct watchdog_device *wdd)
+{
+	return 0;
+}
+
+static const struct watchdog_ops ixp4xx_wdt_restart_only_ops = {
+	.start = ixp4xx_wdt_dummy,
+	.stop = ixp4xx_wdt_dummy,
+	.restart = ixp4xx_wdt_restart,
+	.owner = THIS_MODULE,
+};
+
 static const struct watchdog_info ixp4xx_wdt_info = {
 	.options = WDIOF_KEEPALIVEPING
 		| WDIOF_MAGICCLOSE
@@ -114,14 +133,17 @@ static const struct watchdog_info ixp4xx_wdt_info = {
 
 static int ixp4xx_wdt_probe(struct platform_device *pdev)
 {
+	static const struct watchdog_ops *iwdt_ops;
 	struct device *dev = &pdev->dev;
 	struct ixp4xx_wdt *iwdt;
 	struct clk *clk;
 	int ret;
 
 	if (!(read_cpuid_id() & 0xf) && !cpu_is_ixp46x()) {
-		dev_err(dev, "Rev. A0 IXP42x CPU detected - watchdog disabled\n");
-		return -ENODEV;
+		dev_err(dev, "Rev. A0 IXP42x CPU detected - only restart supported\n");
+		iwdt_ops = &ixp4xx_wdt_restart_only_ops;
+	} else {
+		iwdt_ops = &ixp4xx_wdt_ops;
 	}
 
 	iwdt = devm_kzalloc(dev, sizeof(*iwdt), GFP_KERNEL);
@@ -141,7 +163,7 @@ static int ixp4xx_wdt_probe(struct platform_device *pdev)
 		iwdt->rate = IXP4XX_TIMER_FREQ;
 
 	iwdt->wdd.info = &ixp4xx_wdt_info;
-	iwdt->wdd.ops = &ixp4xx_wdt_ops;
+	iwdt->wdd.ops = iwdt_ops;
 	iwdt->wdd.min_timeout = 1;
 	iwdt->wdd.max_timeout = U32_MAX / iwdt->rate;
 	iwdt->wdd.parent = dev;

---
base-commit: 0bb80ecc33a8fb5a682236443c1e740d5c917d1d
change-id: 20230924-ixp4xx-wdt-restart-d6bf28493173

Best regards,
-- 
Linus Walleij <linus.walleij@linaro.org>