6.6-stable review patch. If anyone has any objections, please let me know.
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From: Aaron Plattner aplattner@nvidia.com
[ Upstream commit 48defdf6b083f74a44e1f742db284960d3444aec ]
The MediaTek implementation of the sbsa_gwdt watchdog has a race condition where a write to SBSA_GWDT_WRR is ignored if it occurs while the hardware is processing a timeout refresh that asserts WS0.
Detect this based on the hardware implementer and adjust wdd->min_hw_heartbeat_ms to avoid the race by forcing the keepalive ping to be one second later.
Signed-off-by: Aaron Plattner aplattner@nvidia.com Acked-by: Timur Tabi ttabi@nvidia.com Reviewed-by: Guenter Roeck linux@roeck-us.net Link: https://lore.kernel.org/r/20250721230640.2244915-1-aplattner@nvidia.com Signed-off-by: Guenter Roeck linux@roeck-us.net Signed-off-by: Wim Van Sebroeck wim@linux-watchdog.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/watchdog/sbsa_gwdt.c | 50 +++++++++++++++++++++++++++++++++--- 1 file changed, 47 insertions(+), 3 deletions(-)
diff --git a/drivers/watchdog/sbsa_gwdt.c b/drivers/watchdog/sbsa_gwdt.c index 5f23913ce3b4..6ce1bfb39064 100644 --- a/drivers/watchdog/sbsa_gwdt.c +++ b/drivers/watchdog/sbsa_gwdt.c @@ -75,11 +75,17 @@ #define SBSA_GWDT_VERSION_MASK 0xF #define SBSA_GWDT_VERSION_SHIFT 16
+#define SBSA_GWDT_IMPL_MASK 0x7FF +#define SBSA_GWDT_IMPL_SHIFT 0 +#define SBSA_GWDT_IMPL_MEDIATEK 0x426 + /** * struct sbsa_gwdt - Internal representation of the SBSA GWDT * @wdd: kernel watchdog_device structure * @clk: store the System Counter clock frequency, in Hz. * @version: store the architecture version + * @need_ws0_race_workaround: + * indicate whether to adjust wdd->timeout to avoid a race with WS0 * @refresh_base: Virtual address of the watchdog refresh frame * @control_base: Virtual address of the watchdog control frame */ @@ -87,6 +93,7 @@ struct sbsa_gwdt { struct watchdog_device wdd; u32 clk; int version; + bool need_ws0_race_workaround; void __iomem *refresh_base; void __iomem *control_base; }; @@ -161,6 +168,31 @@ static int sbsa_gwdt_set_timeout(struct watchdog_device *wdd, */ sbsa_gwdt_reg_write(((u64)gwdt->clk / 2) * timeout, gwdt);
+ /* + * Some watchdog hardware has a race condition where it will ignore + * sbsa_gwdt_keepalive() if it is called at the exact moment that a + * timeout occurs and WS0 is being asserted. Unfortunately, the default + * behavior of the watchdog core is very likely to trigger this race + * when action=0 because it programs WOR to be half of the desired + * timeout, and watchdog_next_keepalive() chooses the exact same time to + * send keepalive pings. + * + * This triggers a race where sbsa_gwdt_keepalive() can be called right + * as WS0 is being asserted, and affected hardware will ignore that + * write and continue to assert WS0. After another (timeout / 2) + * seconds, the same race happens again. If the driver wins then the + * explicit refresh will reset WS0 to false but if the hardware wins, + * then WS1 is asserted and the system resets. + * + * Avoid the problem by scheduling keepalive heartbeats one second later + * than the WOR timeout. + * + * This workaround might not be needed in a future revision of the + * hardware. + */ + if (gwdt->need_ws0_race_workaround) + wdd->min_hw_heartbeat_ms = timeout * 500 + 1000; + return 0; }
@@ -202,12 +234,15 @@ static int sbsa_gwdt_keepalive(struct watchdog_device *wdd) static void sbsa_gwdt_get_version(struct watchdog_device *wdd) { struct sbsa_gwdt *gwdt = watchdog_get_drvdata(wdd); - int ver; + int iidr, ver, impl;
- ver = readl(gwdt->control_base + SBSA_GWDT_W_IIDR); - ver = (ver >> SBSA_GWDT_VERSION_SHIFT) & SBSA_GWDT_VERSION_MASK; + iidr = readl(gwdt->control_base + SBSA_GWDT_W_IIDR); + ver = (iidr >> SBSA_GWDT_VERSION_SHIFT) & SBSA_GWDT_VERSION_MASK; + impl = (iidr >> SBSA_GWDT_IMPL_SHIFT) & SBSA_GWDT_IMPL_MASK;
gwdt->version = ver; + gwdt->need_ws0_race_workaround = + !action && (impl == SBSA_GWDT_IMPL_MEDIATEK); }
static int sbsa_gwdt_start(struct watchdog_device *wdd) @@ -299,6 +334,15 @@ static int sbsa_gwdt_probe(struct platform_device *pdev) else wdd->max_hw_heartbeat_ms = GENMASK_ULL(47, 0) / gwdt->clk * 1000;
+ if (gwdt->need_ws0_race_workaround) { + /* + * A timeout of 3 seconds means that WOR will be set to 1.5 + * seconds and the heartbeat will be scheduled every 2.5 + * seconds. + */ + wdd->min_timeout = 3; + } + status = readl(cf_base + SBSA_GWDT_WCS); if (status & SBSA_GWDT_WCS_WS1) { dev_warn(dev, "System reset by WDT.\n");