Re: [PATCH v3 1/9] platform/x86: dell-descriptor: Use new buffer-based WMI API

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

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On Tue, 31 Mar 2026, Armin Wolf wrote:

> Am 31.03.26 um 11:44 schrieb Ilpo Järvinen:
> 
> > On Sat, 14 Mar 2026, 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   | 94 +++++++++----------
> > >   1 file changed, 47 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..fe42eb8bbd79 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 {
> > > +	char vendor_signature[4];
> > > +	char object_signature[4];
> > > +	__le32 interface_version;
> > > +	__le32 buffer_length;
> > > +	__le32 hotfix_number;
> > > +} __packed;
> > > +
> > >   struct descriptor_priv {
> > >   	struct list_head list;
> > >   	u32 interface_version;
> > > @@ -88,76 +106,58 @@ 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)) {
> > Hi again,
> > 
> > Thinking some more of this...
> > 
> > Since many of these drivers will need to do this size check and assign
> > into some variable that is different from the one passed to
> > wmidev_query_block(), would it make sense to move those into generic code?
> > It probably requires a macro so you'd have access to type information.
> 
> You mean something like wmidev_block_query_sized(wdev, instance, size)?

So this would return ERR_PTR() as I see no out param given to it?

> Personally i see little benefit in having the assignment handled by a macro.

I was not so interested in assignment itself but getting the size 
information from the output type directly but if you prefer writing 
sizeof(*xx), not a big deal to me.

-- 
 i.