Re: [PATCH v3] watchdog: Add driver for Gunyah Watchdog
From: Guenter Roeck
Date: Tue Oct 28 2025 - 13:29:35 EST
On 10/28/25 09:40, Pavan Kondeti wrote:
On Tue, Oct 28, 2025 at 09:06:12AM -0700, Guenter Roeck wrote:
On 10/28/25 02:35, Hrishabh Rajput via B4 Relay wrote:
From: Hrishabh Rajput <hrishabh.rajput@xxxxxxxxxxxxxxxx>
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 Qualcomm watchdog or ARM SBSA watchdog device to be present in
the devicetree. If we detect either of the device nodes, 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@xxxxxxxxxxxxxxxx>
---
...
The Gunyah WDT node gets overlayed by bootloader. We see that this+ gunyah_wdt_dev = platform_device_register_simple(GUNYAH_WDT_DRV_NAME,
+ -1, NULL, 0);
I did not follow the discussion around this, so I may be missing something.
If so, apologies.
This is a highly unusual approach. What is the point of not instantiating
the watchdog device through devicetree and doing it in the init function
instead ? There should be a devicetree node which instantiates the device;
it should never be instantiated from the init function unless there _is_
no devicetree, which is obviously not the case here.
Every other driver which supports devicetree has an .of_match_table
which triggers device instantiation. If the Gunyah watchdog can for
some reason not use that approach, its devicetree description should
be fixed. Instantiating the device from its init function because its
devicetree description is bad or missing is just wrong. It is even more
wrong to try to contact the hardware or embedded controller to figure out
if the device is there. This can have all kinds of negative impact on other
hardware.
overlay is failing w/ upstream device tree since the overlay has
references to downstream code. Please see [1]. Hence we are trying to
register the platform device dynamically.
This is just wrong. Whatever happens downstream is not an upstream concern.
If an overlay is broken, fix it.
NACK to the current approach.
Guenter