linux-kernel - Re: [PATCH v2] watchdog: Add driver for Gunyah Watchdog

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Message-ID: <2e926e17-f8c1-47cf-8864-b0ef97b145ff@oss.qualcomm.com>
Date: Mon, 6 Oct 2025 15:47:55 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: hrishabh.rajput@....qualcomm.com, Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck
 <linux@...ck-us.net>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, linux-watchdog@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pavan Kondeti <pavan.kondeti@....qualcomm.com>,
        Neil Armstrong <neil.armstrong@...aro.org>
Subject: Re: [PATCH v2] watchdog: Add driver for Gunyah Watchdog

On 10/6/25 9:37 AM, Hrishabh Rajput via B4 Relay wrote:
> From: Hrishabh Rajput <hrishabh.rajput@....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.
> 
> When Gunyah is not present or Gunyah emulates MMIO-based watchdog, we
> expect MMIO watchdog device to be present in the devicetree. If we
> detect this device node, we don't proceed ahead. Otherwise, we go ahead
> and invoke GUNYAH_WDT_STATUS SMC to initiate the discovery of the
> SMC-based watchdog.
> 
> Add driver to support the SMC-based watchdog provided by the Gunyah
> Hypervisor. module_exit() is intentionally not implemented as this
> driver is intended to be a persistent module.
> 
> Signed-off-by: Hrishabh Rajput <hrishabh.rajput@....qualcomm.com>
> ---

[...]

> +enum gunyah_error {
> +	GUNYAH_ERROR_OK				= 0,
> +	GUNYAH_ERROR_UNIMPLEMENTED		= -1,
> +	GUNYAH_ERROR_RETRY			= -2,
> +
> +	GUNYAH_ERROR_ARG_INVAL			= 1,
> +	GUNYAH_ERROR_ARG_SIZE			= 2,
> +	GUNYAH_ERROR_ARG_ALIGN			= 3,
> +
> +	GUNYAH_ERROR_NOMEM			= 10,
> +
> +	GUNYAH_ERROR_ADDR_OVFL			= 20,
> +	GUNYAH_ERROR_ADDR_UNFL			= 21,
> +	GUNYAH_ERROR_ADDR_INVAL			= 22,
> +
> +	GUNYAH_ERROR_DENIED			= 30,
> +	GUNYAH_ERROR_BUSY			= 31,
> +	GUNYAH_ERROR_IDLE			= 32,
> +
> +	GUNYAH_ERROR_IRQ_BOUND			= 40,
> +	GUNYAH_ERROR_IRQ_UNBOUND		= 41,
> +
> +	GUNYAH_ERROR_CSPACE_CAP_NULL		= 50,
> +	GUNYAH_ERROR_CSPACE_CAP_REVOKED		= 51,
> +	GUNYAH_ERROR_CSPACE_WRONG_OBJ_TYPE	= 52,
> +	GUNYAH_ERROR_CSPACE_INSUF_RIGHTS	= 53,
> +	GUNYAH_ERROR_CSPACE_FULL		= 54,
> +
> +	GUNYAH_ERROR_MSGQUEUE_EMPTY		= 60,
> +	GUNYAH_ERROR_MSGQUEUE_FULL		= 61,
> +};

Can the calls we make in this driver produce all of these errors?

I'm asking only because we want to minimize the footprint

[...]

> +static unsigned int gunyah_wdt_get_timeleft(struct watchdog_device *wdd)
> +{
> +	struct arm_smccc_res res;
> +	unsigned int seconds_since_last_ping;
> +	int ret;
> +
> +	ret = gunyah_wdt_call(GUNYAH_WDT_STATUS, 0, 0, &res);
> +	if (ret)
> +		return 0;
> +
> +	seconds_since_last_ping = res.a2 / 1000;

> +static int __init gunyah_wdt_init(void)
> +{
> +	struct arm_smccc_res res;
> +	struct watchdog_device *wdd;
> +	struct device_node *np;
> +	int ret;
> +
> +	np = of_find_compatible_node(NULL, NULL, "qcom,kpss-wdt");
> +	if (np) {
> +		of_node_put(np);
> +		return -ENODEV;
> +	}
> +
> +	np = of_find_compatible_node(NULL, NULL, "arm,sbsa-gwdt");
> +	if (np) {
> +		of_node_put(np);
> +		return -ENODEV;
> +	}

Please add a comment about how the above two compatibles tie into our logic
(e.g. "Some builds of Gunyah expose a memory-mapped legacy-Qualcomm or Arm
SBSA watchdog instance instead")

Konrad