Re: [PATCH 6/9] hwmon: (dell-smm) Use new buffer-based WMI API

[Armin Wolf <W_Armin@gmx.de>]

Am 08.03.26 um 15:52 schrieb Guenter Roeck:

> On 3/7/26 16:25, Armin Wolf wrote:
>> Use the new buffer-based WMI API to also support ACPI firmware
>> implementations that do not use ACPI buffers for returning the
>> results of a SMM call.
>>
>> Signed-off-by: Armin Wolf <W_Armin@gmx.de>
>> ---
>>   drivers/hwmon/dell-smm-hwmon.c | 47 ++++++++++++----------------------
>>   1 file changed, 16 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/hwmon/dell-smm-hwmon.c 
>> b/drivers/hwmon/dell-smm-hwmon.c
>> index 038edffc1ac7..07c05a82dc26 100644
>> --- a/drivers/hwmon/dell-smm-hwmon.c
>> +++ b/drivers/hwmon/dell-smm-hwmon.c
>> @@ -12,8 +12,9 @@
>>     #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>>   -#include <linux/acpi.h>
>> +#include <linux/align.h>
>>   #include <linux/capability.h>
>> +#include <linux/compiler_attributes.h>
>>   #include <linux/cpu.h>
>>   #include <linux/ctype.h>
>>   #include <linux/delay.h>
>> @@ -36,10 +37,10 @@
>>   #include <linux/thermal.h>
>>   #include <linux/types.h>
>>   #include <linux/uaccess.h>
>> +#include <linux/unaligned.h>
>>   #include <linux/wmi.h>
>>     #include <linux/i8k.h>
>> -#include <linux/unaligned.h>
>>     #define I8K_SMM_FN_STATUS    0x0025
>>   #define I8K_SMM_POWER_STATUS    0x0069
>> @@ -232,7 +233,7 @@ static const struct dell_smm_ops i8k_smm_ops = {
>>   /*
>>    * Call the System Management Mode BIOS over WMI.
>>    */
>> -static ssize_t wmi_parse_register(u8 *buffer, u32 length, unsigned 
>> int *reg)
>> +static ssize_t wmi_parse_register(void *buffer, size_t length, 
>> unsigned int *reg)
>
> Later in this function:
>
>         memcpy_and_pad(&value, sizeof(value), buffer + 
> sizeof(reg_size), reg_size, 0);
>
> So the new code relies on pointer arithmetic on void *. This used to 
> be invalid,
> and it seems fragile.

I see, good catch. I will keep "buffer" as a u8 pointer then.

Thanks,
Armin Wolf

>
>>   {
>>       __le32 value;
>>       u32 reg_size;
>> @@ -253,7 +254,7 @@ static ssize_t wmi_parse_register(u8 *buffer, u32 
>> length, unsigned int *reg)
>>       return reg_size + sizeof(reg_size);
>>   }
>>   -static int wmi_parse_response(u8 *buffer, u32 length, struct 
>> smm_regs *regs)
>> +static int wmi_parse_response(void *buffer, size_t length, struct 
>> smm_regs *regs)
>
> Same here.
>
> Given that those are internal functions, I don't really see the point 
> of changing
> the parameter type.
>
> Thanks,
> Guenter
>
>>   {
>>       unsigned int *registers[] = {
>>           &regs->eax,
>> @@ -261,7 +262,7 @@ static int wmi_parse_response(u8 *buffer, u32 
>> length, struct smm_regs *regs)
>>           &regs->ecx,
>>           &regs->edx
>>       };
>> -    u32 offset = 0;
>> +    size_t offset = 0;
>>       ssize_t ret;
>>       int i;
>>   @@ -273,19 +274,16 @@ static int wmi_parse_response(u8 *buffer, u32 
>> length, struct smm_regs *regs)
>>           if (ret < 0)
>>               return ret;
>>   -        offset += ret;
>> +        /* WMI aligns u32 integers on a 4 byte boundary */
>> +        offset = ALIGN(offset + ret, 4);
>>       }
>>   -    if (offset != length)
>> -        return -ENOMSG;
>> -
>>       return 0;
>>   }
>>     static int wmi_smm_call(struct device *dev, struct smm_regs *regs)
>>   {
>>       struct wmi_device *wdev = container_of(dev, struct wmi_device, 
>> dev);
>> -    struct acpi_buffer out = { ACPI_ALLOCATE_BUFFER, NULL };
>>       u32 wmi_payload[] = {
>>           sizeof(regs->eax),
>>           regs->eax,
>> @@ -296,32 +294,19 @@ static int wmi_smm_call(struct device *dev, 
>> struct smm_regs *regs)
>>           sizeof(regs->edx),
>>           regs->edx
>>       };
>> -    const struct acpi_buffer in = {
>> +    const struct wmi_buffer in = {
>>           .length = sizeof(wmi_payload),
>> -        .pointer = &wmi_payload,
>> +        .data = &wmi_payload,
>>       };
>> -    union acpi_object *obj;
>> -    acpi_status status;
>> +    struct wmi_buffer out;
>>       int ret;
>>   -    status = wmidev_evaluate_method(wdev, 0x0, 
>> DELL_SMM_LEGACY_EXECUTE, &in, &out);
>> -    if (ACPI_FAILURE(status))
>> -        return -EIO;
>> -
>> -    obj = out.pointer;
>> -    if (!obj)
>> -        return -ENODATA;
>> -
>> -    if (obj->type != ACPI_TYPE_BUFFER) {
>> -        ret = -ENOMSG;
>> -
>> -        goto err_free;
>> -    }
>> -
>> -    ret = wmi_parse_response(obj->buffer.pointer, 
>> obj->buffer.length, regs);
>> +    ret = wmidev_invoke_method(wdev, 0x0, DELL_SMM_LEGACY_EXECUTE, 
>> &in, &out);
>> +    if (ret < 0)
>> +        return ret;
>>   -err_free:
>> -    kfree(obj);
>> +    ret = wmi_parse_response(out.data, out.length,  regs);
>> +    kfree(out.data);
>>         return ret;
>>   }
>
>