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

[Mario Limonciello]

On 4/8/26 06:17, Jack Wu wrote:
> [You don't often get email from wojackbb@xxxxxxxxx. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
>
> 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.
>
> Signed-off-by: Jack Wu <jackbb_wu@xxxxxxxxxx>
> ---
>   drivers/platform/x86/dell/Kconfig             |   6 +
>   drivers/platform/x86/dell/Makefile            |   2 +
>   .../platform/x86/dell/dell-dw5826e-reset.c    | 120 ++++++++++++++++++
>   3 files changed, 128 insertions(+)
>   create mode 100644 drivers/platform/x86/dell/dell-dw5826e-reset.c
>
> 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..28865a123c63
> --- /dev/null
> +++ b/drivers/platform/x86/dell/dell-dw5826e-reset.c
> @@ -0,0 +1,120 @@
> +// 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/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/acpi.h>
> +#include <linux/miscdevice.h>
> +#include <linux/fs.h>
> +#include <linux/uaccess.h>
> +
> +static guid_t palc_dsm_guid =
> +       GUID_INIT(0x5a1a4bba, 0x8006, 0x487e, 0xbe, 0x0a, 0xac, 0xf5, 0xd8, 0xfd, 0xfe, 0x59);
> +
> +struct palc_dev {
> +       struct device *dev;
> +       acpi_handle handle;
> +       struct miscdevice miscdev;
> +};
> +
> +static int trigger_palc_pldr(struct palc_dev *palc)
> +{
> +       union acpi_object *obj;
> +
> +       dev_info(palc->dev, "Triggering PLDR via ACPI _DSM Function 1...\n");

Besides Ilpo's comments - this is pretty noisy.  Do you really need to 
output to the logs every time it's triggered?

> +
> +       obj = acpi_evaluate_dsm(palc->handle, &palc_dsm_guid, 1, 1, NULL);
> +
> +       if (!obj) {
> +               dev_err(palc->dev, "Failed to evaluate _DSM\n");
> +               return -EIO;
> +       }
> +
> +       if (obj->type == ACPI_TYPE_BUFFER)
> +               dev_info(palc->dev, "PLDR _DSM executed successfully\n");

Doesn't this mean it be a failure of obj->type != ACPI_TYPE_BUFFER? 
Presumably you need to set a different return code in this case so the 
caller knows.

> +
> +       ACPI_FREE(obj);
> +       return 0;
> +}
> +
> +static ssize_t palc_write(struct file *filp, const char __user *buf, size_t count, loff_t *ppos)
> +{
> +       struct palc_dev *palc = filp->private_data;
> +
> +       trigger_palc_pldr(palc);

You're ignoring the return code.

> +
> +       return count;
> +}
> +
> +static int palc_open(struct inode *inode, struct file *filp)
> +{
> +       struct palc_dev *palc = container_of(filp->private_data, struct palc_dev, miscdev);
> +
> +       filp->private_data = palc;
> +       return 0;
> +}
> +
> +static const struct file_operations palc_fops = {
> +       .owner  = THIS_MODULE,
> +       .open   = palc_open,
> +       .write  = palc_write,
> +};

Given this is really just triggering an ACPI method and totally ignoring 
user data, maybe a more trivial sysfs file using the various macros is 
useful here instead of all this boilerplate.

> +
> +static int palc_acpi_probe(struct acpi_device *adev)
> +{
> +       struct palc_dev *palc;
> +
> +       palc = devm_kzalloc(&adev->dev, sizeof(*palc), GFP_KERNEL);
> +       if (!palc)
> +               return -ENOMEM;
> +
> +       palc->dev    = &adev->dev;
> +       palc->handle = adev->handle;
> +
> +       palc->miscdev.minor  = MISC_DYNAMIC_MINOR;
> +       palc->miscdev.name   = "reset_palc";
> +       palc->miscdev.fops   = &palc_fops;
> +       palc->miscdev.parent = &adev->dev;
> +
> +       if (misc_register(&palc->miscdev))
> +               return -EINVAL;
> +
> +       dev_set_drvdata(&adev->dev, palc);
> +
> +       dev_info(&adev->dev, "DW5826e Reset Device (PALC0001) Driver Loaded\n");
> +       return 0;
> +}
> +
> +static void palc_acpi_remove(struct acpi_device *adev)
> +{
> +       struct palc_dev *palc = dev_get_drvdata(&adev->dev);
> +
> +       if (palc)
> +               misc_deregister(&palc->miscdev);
> +}
> +
> +static const struct acpi_device_id palc_acpi_ids[] = {
> +       { "PALC0001", 0 },
> +       { "", 0 }
> +};
> +
> +static struct acpi_driver palc_acpi_driver = {
> +       .name  = "palc_reset",
> +       .ids   = palc_acpi_ids,
> +       .ops = {
> +               .add    = palc_acpi_probe,
> +               .remove = palc_acpi_remove,
> +       },
> +};
> +
> +MODULE_DEVICE_TABLE(acpi, palc_acpi_ids);
> +module_acpi_driver(palc_acpi_driver);
> +
> +MODULE_DESCRIPTION("Dell DW5826e reset driver");
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("JackBB Wu");
> --
> 2.34.1