RE: [PATCH] acpi, nfit: fix the memory error check in nfit_handle_mce

["Luck, Tony" <tony.luck@intel.com>]

>> > +       if (!(mce->status & 0xef80) == BIT(7))
>> 
>> Can we get a define for this, or a comment explaining all the magic
>> that's happening on that one line?
>
> Yes - also like lkp pointed out, the check isn't correct at all. Let me
> figure out what really needs to be done, and I will resend with a better
> comment. 

Needs extra parentheses to make it right. Vishal, sorry I led you astray.

	if (!((mce->status & 0xef80) == BIT(7)))

The magic is shown in table 15-9 of the Intel Software Developers Manual
(but perhaps not well explained there).

mce->status in the above code is a value plucked from a machine check
bank status register. See figure 15-6 in the SDM.  The important bits for this
are {15:0} which are the "MCA Error code".  Table 15-9 shows how these
are grouped into types, where the type is defined by the most significant '1'
bit in the field (excluding bit 12 which is the Correction Report Filtering bit,
see section 15.9.2.1).

So if BIT(3) is the most significant bit, the this is a "Generic Cache Hierarchy"
error, BIT(4) denotes a TLB error, BIT(7) a Memory error, and so on.

Maybe we should have defines in mce.h for them?  It gets a bit more complicated
as all the above only applies to Intel branded X86 CPUs ... on AMD different
decoding rules apply.

-Tony


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