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SubjectRe: [PATCH v4 3/3] mailbox: ACPI: erroneous error message when parsing the ACPI, PCCT
Date
On Thursday, May 17, 2018 9:48:39 PM CEST Prakash, Prashanth wrote:
>
> On 5/17/2018 4:24 AM, Rafael J. Wysocki wrote:
> > 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.
>
> Looks good.
>
> Reviewed-by: Prashanth Prakash <pprakash@codeaurora.org>

Applied, thanks!


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