Re: How to detect Cherry Trail vs Brasswell inside the kernel ?

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi,

On 1/6/21 3:59 PM, Peter Zijlstra wrote:
> On Wed, Jan 06, 2021 at 01:31:46PM +0100, Hans de Goede wrote:
>> Hi All,
>>
>> I've 2 different kernel bugs where the fix requires differentiating between
>> Cherry Trail vs Brasswell, just checking the CPU model does not allow to
>> differentiate between these 2 since they are both using Airmont cores.
>>
>> I have the same issue with the Bay Trail laptop SoCs vs the
>> Bay Trail-T tablet SoCs, but for now lets focus on
>> Cherry Trail vs Brasswell since that is less confusing:
>>
>> https://ark.intel.com/content/www/us/en/ark/products/codename/46629/cherry-trail.html
>> https://ark.intel.com/content/www/us/en/ark/products/codename/66094/braswell.html
>>
>> So I see a number of possible solutions here:
>>
>> 1) Do a (substring) check on the CPU model-name checking for "x5-Z8" and "x7-Z8"
>> 2) Check for presence of some embedded peripheral which is present on one but not the
>> other. E.g. The Braswell devices have HDA audio where as the Cherry Trail devices
>> use the "Low Power Engine (LPE) Audio Controller"
>> 3) Check for acpi_gbl_reduced_hardware, but I'm not sure if that is a reliable
>> indicator of running on the tablet versions of the SoCs.
>>
>> 1 and 2 will work but neither is very pretty, I guess I could try to spend some
>> more time investigating 3. But I only have limited access to the non tablet versions
>> of the Bay Trail and I'm not sure if I have any Braswell devices at all. 
>>
>> So I was wondering if anyone else has any better ideas here?
> 
> Does MSR_PLATFORM_ID (0x17) bits 50-52 work to differentiate these?

Thank you, that is (was) a good idea.

So since you send this email I've added a debug print to the kernel for these
bits and collected the output of that debug print on various devices.

Unfortunately these bits always read 0 on all Bay Trail / Bay Trail-T /
Cherry Trail devices which I've tested, so these bits do not help.

Regards,

Hans




[Index of Archives]     [Linux Kernel Development]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux