linux-kernel - Re: [PATCH v2] watchdog: imx7ulp_wdt: Keep WDOG running until A55 enters WFI on i.MX94

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <1ded7e75-67e6-48ab-b63b-e9e38559f26b@roeck-us.net>
Date: Thu, 5 Feb 2026 17:11:58 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: "Peng Fan (OSS)" <peng.fan@....nxp.com>,
 Wim Van Sebroeck <wim@...ux-watchdog.org>, Frank Li <Frank.Li@....com>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>
Cc: linux-watchdog@...r.kernel.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Ranjani Vaidyanathan <ranjani.vaidyanathan@....com>,
 Peng Fan <peng.fan@....com>
Subject: Re: [PATCH v2] watchdog: imx7ulp_wdt: Keep WDOG running until A55
 enters WFI on i.MX94

On 2/5/26 16:23, Peng Fan (OSS) wrote:
> From: Ranjani Vaidyanathan <ranjani.vaidyanathan@....com>
> 
> On i.MX94, watchdog sources clock from bus clock that will be always on
> during the lifecycle of Linux. There is a Low Power Clock Gating(LPCG)
> between the bus clock and watchdog, but the LPCG is not exported for
> software to control, it is hardware automatically controlled. When
> Cortex-A55 executes WFI during suspend flow, the LPCG will automatically
> gate off the clock to stop watchdog and resume clock when Cortex-A55 is
> woke up.
> 
> So watchdog could always be alive to protect Linux, except Cortex-A
> platform WFI is executed in Linux suspend flow.
> 
> Introduce a new hardware feature flag to indicate CPU low-power-mode
> auto clock gating support, and use it to avoid stopping the watchdog
> during suspend when LPCG can safely keep it running.
> 
> Add i.MX94-specific watchdog hardware data and DT compatible entry to
> enable this behavior.
> 
> Signed-off-by: Ranjani Vaidyanathan <ranjani.vaidyanathan@....com>
> [peng.fan@....com: rewrite commit log for clarity]
> Signed-off-by: Peng Fan <peng.fan@....com>

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
> Changes in v2:
> - Update commit log for clarity
> - Link to v1: https://lore.kernel.org/r/20260203-imx94-wdog-v1-1-7deb76dbe350@nxp.com
> ---
>   drivers/watchdog/imx7ulp_wdt.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/imx7ulp_wdt.c b/drivers/watchdog/imx7ulp_wdt.c
> index 03479110453ce78a6a89ce8d351ba9ece2f5e2c5..0ae4c0c00138e89854f14edca0fd5fa84591c2d2 100644
> --- a/drivers/watchdog/imx7ulp_wdt.c
> +++ b/drivers/watchdog/imx7ulp_wdt.c
> @@ -56,6 +56,7 @@ MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default="
>   struct imx_wdt_hw_feature {
>   	bool prescaler_enable;
>   	bool post_rcs_wait;
> +	bool cpu_lpm_auto_cg;
>   	u32 wdog_clock_rate;
>   };
>   
> @@ -360,7 +361,8 @@ static int __maybe_unused imx7ulp_wdt_suspend_noirq(struct device *dev)
>   {
>   	struct imx7ulp_wdt_device *imx7ulp_wdt = dev_get_drvdata(dev);
>   
> -	if (watchdog_active(&imx7ulp_wdt->wdd))
> +
> +	if (watchdog_active(&imx7ulp_wdt->wdd) && !imx7ulp_wdt->hw->cpu_lpm_auto_cg)
>   		imx7ulp_wdt_stop(&imx7ulp_wdt->wdd);
>   
>   	clk_disable_unprepare(imx7ulp_wdt->clk);
> @@ -408,10 +410,17 @@ static const struct imx_wdt_hw_feature imx93_wdt_hw = {
>   	.wdog_clock_rate = 125,
>   };
>   
> +static const struct imx_wdt_hw_feature imx94_wdt_hw = {
> +	.prescaler_enable = true,
> +	.wdog_clock_rate = 125,
> +	.cpu_lpm_auto_cg = true,
> +};
> +
>   static const struct of_device_id imx7ulp_wdt_dt_ids[] = {
>   	{ .compatible = "fsl,imx7ulp-wdt", .data = &imx7ulp_wdt_hw, },
>   	{ .compatible = "fsl,imx8ulp-wdt", .data = &imx8ulp_wdt_hw, },
>   	{ .compatible = "fsl,imx93-wdt", .data = &imx93_wdt_hw, },
> +	{ .compatible = "fsl,imx94-wdt", .data = &imx94_wdt_hw, },
>   	{ /* sentinel */ }
>   };
>   MODULE_DEVICE_TABLE(of, imx7ulp_wdt_dt_ids);
> 
> ---
> base-commit: 193579fe01389bc21aff0051d13f24e8ea95b47d
> change-id: 20260203-imx94-wdog-1e0aa14d661b
> 
> Best regards,