Re: [PATCH] platform/x86/dell: Set USTT mode according to BIOS after reboot

[Shyam Sundar S K <Shyam-sundar.S-k@amd.com>]

Hi Lyndon,

On 9/16/2025 00:24, Lyndon Sanche wrote:
> On Mon, Sep 15, 2025, at 3:41 AM, Shyam Sundar S K wrote:
>> After a reboot, if the user changes the thermal setting in the BIOS, the
>> BIOS applies this change. However, the current `dell-pc` driver does not
>> recognize the updated USTT value, resulting in inconsistent thermal
>> profiles between Windows and Linux.
>>
>> To ensure alignment with Windows behavior, the proposed change involves
>> reading the current USTT setting during driver initialization and updating
>> the dell-pc USTT profile accordingly whenever a change is detected.
> 
> Hello:
> 
> Thank you for the patch. I think I need help understanding why this is not working currently, as this is implemented in the thermal_get_mode functionality.

Okay. Let me elaborate:

There are scenarios where the Dell BIOS needs to send specific events
to the AMD PMF driver. The `amd_pmf` driver registers a handler with
the ACPI subsystem to listen for these events, which should originate
from the `dell_pc` driver. However, during probe time, the `dell_pc`
driver lacks awareness of any changes to the USTT value. As a result,
it may report outdated USTT data, leading to incorrect thermal
configurations.

Further debug revealed that Windows adjust to changes in USTT and
behave accordingly.

To align with Windows behavior, we now read the current USTT value
during the `dell_pc` driver's probe phase. This ensures that any
updates are captured, enabling the `amd_pmf` driver to receive
accurate information through the ACPI events it listens to.

> 
> This change, upon my first read, seems to read the mode from the BIOS and then write what it read back to the BIOS. Is my understanding correct?
Yes, via the dell_smbios_*() calls.

> I do not have a computer where I can change the mode from the BIOS, so I cannot test that specific case.
Okay. Alex (Cc'ed) from Dell has tested this on Multiple platforms.

> What does the platform_profile get set to on boot without this patch?

"custom"

Thanks,
Shyam