Re: [PATCH v6 1/2] platform/x86: dell-dw5826e: Add reset driver for DW5826e

[Ilpo Järvinen]

On Mon, 4 May 2026, Jack Wu wrote:

> If the DW5826e is in a frozen state and unable to receive USB commands,
> this driver provides a method for the user to reset the DW5826e via ACPI.
> 
> E.g: echo 1 > /sys/bus/platform/devices/PALC0001\:00/wwan_reset
> 
> Reviewed-by: Mario Limonciello (AMD) <superm1@xxxxxxxxxx>
> Reviewed-by: Armin Wolf <W_Armin@xxxxxx>
> Signed-off-by: Jack Wu <jackbb_wu@xxxxxxxxxx>
> ---
> v6:
>   - Use same define for the DSM check
> v5:
>   - Use BIT() for the DSM method
> v4:
>   - Fix version of the ABI documentation to 7.2
>   - Add include linux/types.h
> v3:
>   - Rename sysfs attribute from "pldr" to "wwan_reset" for clarity
>   - Add ABI documentation for the wwan_reset sysfs interface
>   - Validate _DSM method availability in probe using acpi_check_dsm()
> v2:
>   - Remove extra empty line
>   - Add missing includes and Remove unnecessary includes, sort includes alphabetically
>   - Remove noisy dev_info()
>   - Handle obj->type != ACPI_TYPE_BUFFER as error with proper return code
>   - Replace miscdevice/file_operations with sysfs attribute (DEVICE_ATTR_WO) to reduce boilerplate
>   - Propagate trigger_palc_pldr() return code to userspace
>   - Convert from acpi_driver to platform_driver
> ---
> ---
>  .../testing/sysfs-driver-dell-dw5826e-reset   |  9 ++
>  drivers/platform/x86/dell/Kconfig             |  6 ++
>  drivers/platform/x86/dell/Makefile            |  2 +
>  .../platform/x86/dell/dell-dw5826e-reset.c    | 93 +++++++++++++++++++
>  4 files changed, 110 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-driver-dell-dw5826e-reset
>  create mode 100644 drivers/platform/x86/dell/dell-dw5826e-reset.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-driver-dell-dw5826e-reset b/Documentation/ABI/testing/sysfs-driver-dell-dw5826e-reset
> new file mode 100644
> index 000000000000..a665e265633f
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-driver-dell-dw5826e-reset
> @@ -0,0 +1,9 @@
> +What:		/sys/bus/platform/devices/<PALC0001 device>/wwan_reset
> +Date:		April 2026

It's already May, and 7.2 won't be out even in May.

> +KernelVersion:	7.2
> +Contact:	Jackbb Wu <jackbb.wu@xxxxxxxxxx>
> +Description:
> +		Writing to this file triggers a Platform Level Device Reset
> +		(PLDR) of the Dell DW5826e WWAN module via an ACPI _DSM
> +		method. This can be used to recover the modem when it is in
> +		a frozen state and unable to respond to USB commands.
> diff --git a/drivers/platform/x86/dell/Kconfig b/drivers/platform/x86/dell/Kconfig
> index 738c108c2163..c4540c837a88 100644
> --- a/drivers/platform/x86/dell/Kconfig
> +++ b/drivers/platform/x86/dell/Kconfig
> @@ -276,4 +276,10 @@ config DELL_WMI_SYSMAN
>  	  To compile this driver as a module, choose M here: the module will
>  	  be called dell-wmi-sysman.
>  
> +config DELL_DW5826E_RESET
> +	tristate "Dell DW5826e PLDR reset support"
> +	default m
> +	depends on ACPI
> +	help
> +	  This adds support for the Dell DW5826e PLDR reset via ACPI
>  endif # X86_PLATFORM_DRIVERS_DELL
> diff --git a/drivers/platform/x86/dell/Makefile b/drivers/platform/x86/dell/Makefile
> index c7501c25e627..8150283cfd1d 100644
> --- a/drivers/platform/x86/dell/Makefile
> +++ b/drivers/platform/x86/dell/Makefile
> @@ -28,3 +28,5 @@ obj-$(CONFIG_DELL_WMI_DESCRIPTOR)		+= dell-wmi-descriptor.o
>  obj-$(CONFIG_DELL_WMI_DDV)			+= dell-wmi-ddv.o
>  obj-$(CONFIG_DELL_WMI_LED)			+= dell-wmi-led.o
>  obj-$(CONFIG_DELL_WMI_SYSMAN)			+= dell-wmi-sysman/
> +obj-$(CONFIG_DELL_DW5826E_RESET)		+= dell-dw5826e-reset.o
> +
> diff --git a/drivers/platform/x86/dell/dell-dw5826e-reset.c b/drivers/platform/x86/dell/dell-dw5826e-reset.c
> new file mode 100644
> index 000000000000..d37c6a66c4c3
> --- /dev/null
> +++ b/drivers/platform/x86/dell/dell-dw5826e-reset.c
> @@ -0,0 +1,93 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + *  dell-dw5826e-reset.c - Dell DW5826e reset driver
> + *
> + *  Copyright (C) 2026 Jackbb Wu <jackbb.wu@xxxxxxxxxx>
> + */
> +
> +#include <linux/acpi.h>
> +#include <linux/bits.h>
> +#include <linux/device.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/types.h>
> +#include <linux/uuid.h>
> +
> +#define PALC_DSM_FN_TRIGGER_PLDR    1

Place BIT() into the define instead (I think I mentioned this already 
earlier), it's used by all sites so there's no good reason to keep in 
inline with the code (AFAICT):

> +	obj = acpi_evaluate_dsm(handle, &palc_dsm_guid, 1, BIT(PALC_DSM_FN_TRIGGER_PLDR), NULL);

> +	if (!acpi_check_dsm(handle, &palc_dsm_guid, 1, BIT(PALC_DSM_FN_TRIGGER_PLDR)))


-- 
 i.