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

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Message-ID: <6e7eaac2-0859-4bfd-b76b-2f81e384a91c@roeck-us.net>
Date: Mon, 6 Oct 2025 07:18:41 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: hrishabh.rajput@....qualcomm.com, Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>,
 Wim Van Sebroeck <wim@...ux-watchdog.org>, 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 00:37, 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>
> ---
> Gunyah is a Type-I hypervisor which was introduced in the patch series
> [1]. It is an open source hypervisor. The source repo is available at
> [2].
> 
> The Gunyah Hypervisor doesn't allow its Virtual Machines to directly
> access the MMIO watchdog. It either provides the fully emulated MMIO
> based watchdog interface or the SMC-based watchdog interface depending
> on the hypervisor configuration.
> The SMC-based watchdog follows ARM's SMC Calling Convention (SMCCC)
> version 1.1 and uses Vendor Specific Hypervisor Service Calls space.
> 
> This patch series adds support for the SMC-based watchdog interface
> provided by the Gunyah Hypervisor.
> 
> This series is tested on SM8750 platform.
> 
> [1]
> https://lore.kernel.org/all/20240222-gunyah-v17-0-1e9da6763d38@quicinc.com/
> 
> [2]
> https://github.com/quic/gunyah-hypervisor
> ---
> Changes in v2:
> - Move away from platform driver model since the devicetree overlay does
>    not happen by default.

This is just wrong. Platform drivers do not depend on devicetree. I am not even
going to review the rest of the driver.

Guenter