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

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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?



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