linux-kernel - [PATCH v2] watchdog: apple: set max_hw_heartbeat_ms instead of max

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Message-ID: <20250506142621.11428-2-flokli@flokli.de>
Date: Tue,  6 May 2025 17:26:22 +0300
From: Florian Klink <flokli@...kli.de>
To: Sven Peter <sven@...npeter.dev>,
	Janne Grunau <j@...nau.net>,
	Alyssa Rosenzweig <alyssa@...enzweig.io>,
	Neal Gompa <neal@...pa.dev>,
	Wim Van Sebroeck <wim@...ux-watchdog.org>,
	Guenter Roeck <linux@...ck-us.net>
Cc: asahi@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-watchdog@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Florian Klink <flokli@...kli.de>
Subject: [PATCH v2] watchdog: apple: set max_hw_heartbeat_ms instead of max_timeout

The hardware only supports timeouts slightly below 3mins, but by using
max_hw_heartbeat_ms we can let the kernel take care of supporting larger
timeouts than that requested from userspace.

Switching to max_hw_heartbeat_ms also means our set_timeout function now
needs to configure the hardware to the minimum of either the requested
timeout (in seconds) or the maximum supported by the user (in seconds).

Signed-off-by: Florian Klink <flokli@...kli.de>
---
Changes in v2:
- Use the minimum of wdd->max_hw_heartbeat_ms / 1000 and
  userspace-requested timeout as documented in watchdog-kernel-api.rst
- Link to v1: https://lore.kernel.org/asahi/20250506120111.5041-1-flokli@flokli.de/
---
 drivers/watchdog/apple_wdt.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/apple_wdt.c b/drivers/watchdog/apple_wdt.c
index 95d9e37df41c..66a158f67a71 100644
--- a/drivers/watchdog/apple_wdt.c
+++ b/drivers/watchdog/apple_wdt.c
@@ -95,9 +95,12 @@ static int apple_wdt_ping(struct watchdog_device *wdd)
 static int apple_wdt_set_timeout(struct watchdog_device *wdd, unsigned int s)
 {
 	struct apple_wdt *wdt = to_apple_wdt(wdd);
+	u32 actual;
 
 	writel_relaxed(0, wdt->regs + APPLE_WDT_WD1_CUR_TIME);
-	writel_relaxed(wdt->clk_rate * s, wdt->regs + APPLE_WDT_WD1_BITE_TIME);
+
+	actual = min(s, wdd->max_hw_heartbeat_ms / 1000);
+	writel_relaxed(wdt->clk_rate * actual, wdt->regs + APPLE_WDT_WD1_BITE_TIME);
 
 	wdd->timeout = s;
 
@@ -177,7 +180,7 @@ static int apple_wdt_probe(struct platform_device *pdev)
 
 	wdt->wdd.ops = &apple_wdt_ops;
 	wdt->wdd.info = &apple_wdt_info;
-	wdt->wdd.max_timeout = U32_MAX / wdt->clk_rate;
+	wdt->wdd.max_hw_heartbeat_ms = U32_MAX / wdt->clk_rate * 1000;
 	wdt->wdd.timeout = APPLE_WDT_TIMEOUT_DEFAULT;
 
 	wdt_ctrl = readl_relaxed(wdt->regs + APPLE_WDT_WD1_CTRL);
-- 
2.49.0