Re: [PATCH 1/9] platform/x86: dell-descriptor: Use new buffer-based WMI API

[Mario Limonciello <mario.limonciello@amd.com>]

On 3/7/2026 6:25 PM, Armin Wolf wrote:
> Use the new buffer-based WMI API to also support ACPI firmware
> implementations that do not use ACPI buffers for the descriptor.
> 
> Signed-off-by: Armin Wolf <W_Armin@gmx.de>
> ---
>   .../platform/x86/dell/dell-wmi-descriptor.c   | 96 ++++++++++---------
>   1 file changed, 49 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/platform/x86/dell/dell-wmi-descriptor.c b/drivers/platform/x86/dell/dell-wmi-descriptor.c
> index c2a180202719..621502368895 100644
> --- a/drivers/platform/x86/dell/dell-wmi-descriptor.c
> +++ b/drivers/platform/x86/dell/dell-wmi-descriptor.c
> @@ -7,7 +7,7 @@
>   
>   #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>   
> -#include <linux/acpi.h>
> +#include <linux/compiler_attributes.h>
>   #include <linux/list.h>
>   #include <linux/module.h>
>   #include <linux/wmi.h>
> @@ -15,6 +15,24 @@
>   
>   #define DELL_WMI_DESCRIPTOR_GUID "8D9DDCBC-A997-11DA-B012-B622A1EF5492"
>   
> +/*
> + * Descriptor buffer is 128 byte long and contains:
> + *
> + *       Name             Offset  Length  Value
> + * Vendor Signature          0       4    "DELL"
> + * Object Signature          4       4    " WMI"
> + * WMI Interface Version     8       4    <version>
> + * WMI buffer length        12       4    <length>
> + * WMI hotfix number        16       4    <hotfix>
> + */
> +struct descriptor {
> +	__le32 vendor_signature;
> +	__le32 object_signature;
> +	__le32 interface_version;
> +	__le32 buffer_length;
> +	__le32 hotfix_number;
> +} __packed;
> +
>   struct descriptor_priv {
>   	struct list_head list;
>   	u32 interface_version;
> @@ -88,76 +106,60 @@ bool dell_wmi_get_hotfix(u32 *hotfix)
>   }
>   EXPORT_SYMBOL_GPL(dell_wmi_get_hotfix);
>   
> -/*
> - * Descriptor buffer is 128 byte long and contains:
> - *
> - *       Name             Offset  Length  Value
> - * Vendor Signature          0       4    "DELL"
> - * Object Signature          4       4    " WMI"
> - * WMI Interface Version     8       4    <version>
> - * WMI buffer length        12       4    <length>
> - * WMI hotfix number        16       4    <hotfix>
> - */
> -static int dell_wmi_descriptor_probe(struct wmi_device *wdev,
> -				     const void *context)
> +static int dell_wmi_descriptor_probe(struct wmi_device *wdev, const void *context)
>   {
> -	union acpi_object *obj = NULL;
>   	struct descriptor_priv *priv;
> -	u32 *buffer;
> +	struct wmi_buffer buffer;
> +	struct descriptor *desc;
>   	int ret;
>   
> -	obj = wmidev_block_query(wdev, 0);
> -	if (!obj) {
> -		dev_err(&wdev->dev, "failed to read Dell WMI descriptor\n");
> -		ret = -EIO;
> -		goto out;
> -	}
> +	ret = wmidev_query_block(wdev, 0, &buffer);
> +	if (ret < 0)
> +		return ret;
>   
> -	if (obj->type != ACPI_TYPE_BUFFER) {
> -		dev_err(&wdev->dev, "Dell descriptor has wrong type\n");
> +	if (buffer.length < sizeof(*desc)) {
> +		dev_err(&wdev->dev,
> +			"Dell descriptor buffer contains not enough data (%zu)\n",
> +			buffer.length);
>   		ret = -EINVAL;
>   		descriptor_valid = ret;
>   		goto out;
>   	}
>   
> -	/* Although it's not technically a failure, this would lead to
> -	 * unexpected behavior
> -	 */
> -	if (obj->buffer.length != 128) {
> -		dev_err(&wdev->dev,
> -			"Dell descriptor buffer has unexpected length (%d)\n",
> -			obj->buffer.length);
> -		ret = -EINVAL;
> +	desc = buffer.data;
> +
> +	/* "DELL" */
> +	if (le32_to_cpu(desc->vendor_signature) != 0x4C4C4544) {

Do you think you could come up with a helper for matching an expected 
"string" like this?  I /suspect/ it's going to be a common pattern that 
vendors use and it will increase code readability going forward if a 
helper is possible.  I see it at least twice in this patch alone.

Something like this prototype:

bool wmi_valid_signature(u32 field, const char* expected_str);


> +		dev_err(&wdev->dev, "Dell descriptor buffer has invalid vendor signature (%u)\n",
> +			le32_to_cpu(desc->vendor_signature));
> +		ret = -ENOMSG;
>   		descriptor_valid = ret;
>   		goto out;
>   	}
>   
> -	buffer = (u32 *)obj->buffer.pointer;
> -
> -	if (strncmp(obj->string.pointer, "DELL WMI", 8) != 0) {
> -		dev_err(&wdev->dev, "Dell descriptor buffer has invalid signature (%8ph)\n",
> -			buffer);
> -		ret = -EINVAL;
> +	/* " WMI" */
> +	if (le32_to_cpu(desc->object_signature) != 0x494D5720) {
> +		dev_err(&wdev->dev, "Dell descriptor buffer has invalid object signature (%u)\n",
> +			le32_to_cpu(desc->object_signature));
> +		ret = -ENOMSG;
>   		descriptor_valid = ret;
>   		goto out;
>   	}
>   	descriptor_valid = 0;
>   
> -	if (buffer[2] != 0 && buffer[2] != 1)
> -		dev_warn(&wdev->dev, "Dell descriptor buffer has unknown version (%lu)\n",
> -			(unsigned long) buffer[2]);
> -
> -	priv = devm_kzalloc(&wdev->dev, sizeof(struct descriptor_priv),
> -	GFP_KERNEL);
> +	if (le32_to_cpu(desc->interface_version) > 2)
> +		dev_warn(&wdev->dev, "Dell descriptor buffer has unknown version (%u)\n",
> +			 le32_to_cpu(desc->interface_version));
>   
> +	priv = devm_kzalloc(&wdev->dev, sizeof(*priv), GFP_KERNEL);
>   	if (!priv) {
>   		ret = -ENOMEM;
>   		goto out;
>   	}
>   
> -	priv->interface_version = buffer[2];
> -	priv->size = buffer[3];
> -	priv->hotfix = buffer[4];
> +	priv->interface_version = le32_to_cpu(desc->interface_version);
> +	priv->size = le32_to_cpu(desc->buffer_length);
> +	priv->hotfix = le32_to_cpu(desc->hotfix_number);
>   	ret = 0;
>   	dev_set_drvdata(&wdev->dev, priv);
>   	mutex_lock(&list_mutex);
> @@ -170,7 +172,7 @@ static int dell_wmi_descriptor_probe(struct wmi_device *wdev,
>   		(unsigned long) priv->hotfix);
>   
>   out:
> -	kfree(obj);
> +	kfree(buffer.data);
>   	return ret;
>   }
>