Re: [PATCH v7 2/2] watchdog: Add driver for Gunyah Watchdog

[Guenter Roeck <linux@roeck-us.net>]

On 11/13/25 23:57, Hrishabh Rajput via B4 Relay wrote:
> From: Hrishabh Rajput <hrishabh.rajput@oss.qualcomm.com>
> 
> On Qualcomm SoCs running under the Gunyah hypervisor, access to watchdog
> through MMIO is not available on all platforms. Depending on the
> hypervisor configuration, the watchdog is either fully emulated or
> exposed via ARM's SMC Calling Conventions (SMCCC) through the Vendor
> Specific Hypervisor Service Calls space.
> 
> Add driver to support the SMC-based watchdog provided by the Gunyah
> Hypervisor. Device registration is done in the QCOM SCM driver after
> checks to restrict the watchdog initialization to Qualcomm devices
> running under Gunyah.
> 
> Gunyah watchdog is not a hardware but an SMC-based vendor-specific
> hypervisor interface provided by the Gunyah hypervisor. The design
> involving QCOM SCM driver for registering the platform device has been
> devised to avoid adding non-hardware nodes to devicetree.
> 
> Signed-off-by: Hrishabh Rajput <hrishabh.rajput@oss.qualcomm.com>
> ---
>   MAINTAINERS                   |   1 +
>   drivers/watchdog/Kconfig      |  13 +++
>   drivers/watchdog/Makefile     |   1 +
>   drivers/watchdog/gunyah_wdt.c | 260 ++++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 275 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index ddecf1ef3bed..f80e762aa324 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3215,6 +3215,7 @@ F:	arch/arm64/boot/dts/qcom/
>   F:	drivers/bus/qcom*
>   F:	drivers/firmware/qcom/
>   F:	drivers/soc/qcom/
> +F:	drivers/watchdog/gunyah_wdt.c
>   F:	include/dt-bindings/arm/qcom,ids.h
>   F:	include/dt-bindings/firmware/qcom,scm.h
>   F:	include/dt-bindings/soc/qcom*
> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> index 05008d937e40..bc6db9a1c116 100644
> --- a/drivers/watchdog/Kconfig
> +++ b/drivers/watchdog/Kconfig
> @@ -2354,4 +2354,17 @@ config KEEMBAY_WATCHDOG
>   	  To compile this driver as a module, choose M here: the
>   	  module will be called keembay_wdt.
>   
> +config GUNYAH_WATCHDOG
> +	tristate "Qualcomm Gunyah Watchdog"
> +	depends on ARCH_QCOM || COMPILE_TEST
> +	depends on HAVE_ARM_SMCCC
> +	select WATCHDOG_CORE
> +	help
> +	  Say Y here to include support for watchdog timer provided by the
> +	  Gunyah hypervisor. The driver uses ARM SMC Calling Convention (SMCCC)
> +	  to interact with Gunyah Watchdog.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called gunyah_wdt.
> +
>   endif # WATCHDOG
> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> index b680e4d3c1bc..1215efb7816d 100644
> --- a/drivers/watchdog/Makefile
> +++ b/drivers/watchdog/Makefile
> @@ -102,6 +102,7 @@ obj-$(CONFIG_MSC313E_WATCHDOG) += msc313e_wdt.o
>   obj-$(CONFIG_APPLE_WATCHDOG) += apple_wdt.o
>   obj-$(CONFIG_SUNPLUS_WATCHDOG) += sunplus_wdt.o
>   obj-$(CONFIG_MARVELL_GTI_WDT) += marvell_gti_wdt.o
> +obj-$(CONFIG_GUNYAH_WATCHDOG) += gunyah_wdt.o
>   
>   # X86 (i386 + ia64 + x86_64) Architecture
>   obj-$(CONFIG_ACQUIRE_WDT) += acquirewdt.o
> diff --git a/drivers/watchdog/gunyah_wdt.c b/drivers/watchdog/gunyah_wdt.c
> new file mode 100644
> index 000000000000..addfd1733ad1
> --- /dev/null
> +++ b/drivers/watchdog/gunyah_wdt.c
> @@ -0,0 +1,260 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
> + */
> +
> +#include <linux/arm-smccc.h>
> +#include <linux/delay.h>
> +#include <linux/errno.h>
> +#include <linux/kernel.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/watchdog.h>
> +
> +#define GUNYAH_WDT_SMCCC_CALL_VAL(func_id) \
> +	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, ARM_SMCCC_SMC_32,\
> +			   ARM_SMCCC_OWNER_VENDOR_HYP, func_id)
> +
> +/* SMCCC function IDs for watchdog operations */
> +#define GUNYAH_WDT_CONTROL   GUNYAH_WDT_SMCCC_CALL_VAL(0x0005)
> +#define GUNYAH_WDT_STATUS    GUNYAH_WDT_SMCCC_CALL_VAL(0x0006)
> +#define GUNYAH_WDT_PING      GUNYAH_WDT_SMCCC_CALL_VAL(0x0007)
> +#define GUNYAH_WDT_SET_TIME  GUNYAH_WDT_SMCCC_CALL_VAL(0x0008)
> +
> +/*
> + * Control values for GUNYAH_WDT_CONTROL.
> + * Bit 0 is used to enable or disable the watchdog. If this bit is set,
> + * then the watchdog is enabled and vice versa.
> + * Bit 1 should always be set to 1 as this bit is reserved in Gunyah and
> + * it's expected to be 1.
> + */
> +#define WDT_CTRL_ENABLE  (BIT(1) | BIT(0))
> +#define WDT_CTRL_DISABLE BIT(1)
> +
> +enum gunyah_error {
> +	GUNYAH_ERROR_OK				= 0,
> +	GUNYAH_ERROR_UNIMPLEMENTED		= -1,
> +	GUNYAH_ERROR_ARG_INVAL			= 1,
> +};
> +
> +/**
> + * gunyah_error_remap() - Remap Gunyah hypervisor errors into a Linux error code
> + * @gunyah_error: Gunyah hypercall return value
> + */
> +static inline int gunyah_error_remap(enum gunyah_error gunyah_error)
> +{
> +	switch (gunyah_error) {
> +	case GUNYAH_ERROR_OK:
> +		return 0;
> +	case GUNYAH_ERROR_UNIMPLEMENTED:
> +		return -EOPNOTSUPP;
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int gunyah_wdt_call(unsigned long func_id, unsigned long arg1,
> +			   unsigned long arg2)
> +{
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_1_1_smc(func_id, arg1, arg2, &res);
> +	return gunyah_error_remap(res.a0);
> +}
> +
> +static int gunyah_wdt_start(struct watchdog_device *wdd)
> +{
> +	unsigned int timeout_ms;
> +	struct device *dev = wdd->parent;
> +	int ret;
> +
> +	ret = gunyah_wdt_call(GUNYAH_WDT_CONTROL, WDT_CTRL_DISABLE, 0);
> +	if (ret && watchdog_active(wdd)) {
> +		dev_err(dev, "%s: Failed to stop gunyah wdt %d\n", __func__, ret);
> +		return ret;
> +	}
> +
> +	timeout_ms = wdd->timeout * 1000;
> +	ret = gunyah_wdt_call(GUNYAH_WDT_SET_TIME, timeout_ms, timeout_ms);
> +	if (ret) {
> +		dev_err(dev, "%s: Failed to set timeout for gunyah wdt %d\n",
> +			__func__, ret);
> +		return ret;
> +	}
> +
> +	ret = gunyah_wdt_call(GUNYAH_WDT_CONTROL, WDT_CTRL_ENABLE, 0);
> +	if (ret)
> +		dev_err(dev, "%s: Failed to start gunyah wdt %d\n", __func__, ret);
> +
> +	return ret;
> +}
> +
> +static int gunyah_wdt_stop(struct watchdog_device *wdd)
> +{
> +	return gunyah_wdt_call(GUNYAH_WDT_CONTROL, WDT_CTRL_DISABLE, 0);
> +}
> +
> +static int gunyah_wdt_ping(struct watchdog_device *wdd)
> +{
> +	return gunyah_wdt_call(GUNYAH_WDT_PING, 0, 0);
> +}
> +
> +static int gunyah_wdt_set_timeout(struct watchdog_device *wdd,
> +				  unsigned int timeout_sec)
> +{
> +	wdd->timeout = timeout_sec;
> +
> +	if (watchdog_active(wdd))
> +		return gunyah_wdt_start(wdd);
> +
> +	return 0;
> +}
> +
> +static int gunyah_wdt_get_time_since_last_ping(void)
> +{
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_1_1_smc(GUNYAH_WDT_STATUS, 0, 0, &res);
> +	if (res.a0)
> +		return gunyah_error_remap(res.a0);
> +
> +	return res.a2 / 1000;
> +}
> +
> +static unsigned int gunyah_wdt_get_timeleft(struct watchdog_device *wdd)
> +{
> +	int seconds_since_last_ping;
> +
> +	seconds_since_last_ping = gunyah_wdt_get_time_since_last_ping();
> +	if (seconds_since_last_ping < 0 ||
> +	    seconds_since_last_ping > wdd->timeout)
> +		return 0;
> +
> +	return wdd->timeout - seconds_since_last_ping;
> +}
> +
> +static int gunyah_wdt_restart(struct watchdog_device *wdd,
> +			      unsigned long action, void *data)
> +{
> +	/* Set timeout to 1ms and send a ping */
> +	gunyah_wdt_call(GUNYAH_WDT_CONTROL, WDT_CTRL_DISABLE, 0);
> +	gunyah_wdt_call(GUNYAH_WDT_SET_TIME, 1, 1);
> +	gunyah_wdt_call(GUNYAH_WDT_CONTROL, WDT_CTRL_ENABLE, 0);
> +	gunyah_wdt_call(GUNYAH_WDT_PING, 0, 0);
> +
> +	/* Wait to make sure reset occurs */
> +	mdelay(100);
> +
> +	return 0;
> +}
> +
> +static const struct watchdog_info gunyah_wdt_info = {
> +	.identity = "Gunyah Watchdog",
> +	.options = WDIOF_SETTIMEOUT
> +		 | WDIOF_KEEPALIVEPING
> +		 | WDIOF_MAGICCLOSE,
> +};
> +
> +static const struct watchdog_ops gunyah_wdt_ops = {
> +	.owner = THIS_MODULE,
> +	.start = gunyah_wdt_start,
> +	.stop = gunyah_wdt_stop,
> +	.ping = gunyah_wdt_ping,
> +	.set_timeout = gunyah_wdt_set_timeout,
> +	.get_timeleft = gunyah_wdt_get_timeleft,
> +	.restart = gunyah_wdt_restart
> +};
> +
> +static int gunyah_wdt_probe(struct platform_device *pdev)
> +{
> +	struct watchdog_device *wdd;
> +	struct device *dev = &pdev->dev;
> +	int ret;
> +
> +	ret = gunyah_wdt_call(GUNYAH_WDT_STATUS, 0, 0);
> +	if (ret) {
> +		dev_err_probe(dev, ret, "status check failed\n");
> +		return ret;

 From the context, it seems to me that this should fail silently with -ENODEV
if the function returns -EOPNOTSUPP (not implemented).

Guenter