On Thu, May 17, 2018 at 12:01 AM, Al Stone <ahs3@xxxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
