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SubjectRe: [PATCH v4 3/3] mailbox: ACPI: erroneous error message when parsing the ACPI, PCCT
On Thu, May 17, 2018 at 12:01 AM, Al Stone <ahs3@redhat.com> wrote:
> There have been multiple reports of the following error message:
>
> [ 0.068293] Error parsing PCC subspaces from PCCT
>
> This error message is not correct. In multiple cases examined, the PCCT
> (Platform Communications Channel Table) concerned is actually properly
> constructed; the problem is that acpi_pcc_probe() which reads the PCCT
> is making the assumption that the only valid PCCT is one that contains
> subtables of one of two types: ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE or
> ACPI_PCCT_TYPE_HW_REDUCED_TYPE2. The number of subtables of these
> types are counted and as long as there is at least one of the desired
> types, the acpi_pcc_probe() succeeds. When no subtables of these types
> are found, regardless of whether or not any other subtable types are
> present, the error mentioned above is reported.
>
> In the cases reported to me personally, the PCCT contains exactly one
> subtable of type ACPI_PCCT_TYPE_GENERIC_SUBSPACE. The function
> acpi_pcc_probe() does not count it as a valid subtable, so believes
> there to be no valid subtables, and hence outputs the error message.
>
> An example of the PCCT being reported as erroneous yet perfectly fine
> is the following:
>
> Signature : "PCCT"
> Table Length : 0000006E
> Revision : 05
> Checksum : A9
> Oem ID : "XXXXXX"
> Oem Table ID : "XXXXX "
> Oem Revision : 00002280
> Asl Compiler ID : "XXXX"
> Asl Compiler Revision : 00000002
>
> Flags (decoded below) : 00000001
> Platform : 1
> Reserved : 0000000000000000
>
> Subtable Type : 00 [Generic Communications Subspace]
> Length : 3E
>
> Reserved : 000000000000
> Base Address : 00000000DCE43018
> Address Length : 0000000000001000
>
> Doorbell Register : [Generic Address Structure]
> Space ID : 01 [SystemIO]
> Bit Width : 08
> Bit Offset : 00
> Encoded Access Width : 01 [Byte Access:8]
> Address : 0000000000001842
>
> Preserve Mask : 00000000000000FD
> Write Mask : 0000000000000002
> Command Latency : 00001388
> Maximum Access Rate : 00000000
> Minimum Turnaround Time : 0000
>
> To fix this, we count up all of the possible subtable types for the
> PCCT, and only report an error when there are none (which could mean
> either no subtables, or no valid subtables), or there are too many.
> We also change the logic so that if there is a valid subtable, we
> do try to initialize it per the PCCT subtable contents. This is a
> change in functionality; previously, the probe would have returned
> right after the error message and would not have tried to use any
> other subtable definition.
>
> Tested on my personal laptop which showed the error previously; the
> error message no longer appears and the laptop appears to operate
> normally.

I'd like to know the Prashanth's opinion here.

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