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SubjectRe: [PATCH v3 3/3] mailbox: ACPI: erroneous error message when parsing the ACPI PCCT
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On 05/15/2018 02:00 AM, Rafael J. Wysocki wrote:
> On Tue, May 15, 2018 at 12:49 AM, Al Stone <ahs3@redhat.com> wrote:
>> On 05/14/2018 03:04 PM, Prakash, Prashanth wrote:
>>>
>>>
>>> On 4/30/2018 6:39 PM, Al Stone 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.
>>>>
>>>> Signed-off-by: Al Stone <ahs3@redhat.com>
>>>> Cc: Jassi Brar <jassisinghbrar@gmail.com>
>>>> Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
>>>> Cc: Len Brown <lenb@kernel.org>
>>>> ---
>>>> drivers/mailbox/pcc.c | 96 +++++++++++++++++++++++++++++++++------------------
>>>> 1 file changed, 63 insertions(+), 33 deletions(-)
>>>>
>>>> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
>>>> index 3ef7f036ceea..72af37d7e95e 100644
>>>> --- a/drivers/mailbox/pcc.c
>>>> +++ b/drivers/mailbox/pcc.c
>>>> @@ -372,13 +372,37 @@ static const struct mbox_chan_ops pcc_chan_ops = {
>>>> .send_data = pcc_send_data,
>>>> };
>>>>
>>>> +/*
>>>> + *
>>>> + * count_pcc_subspaces -- Count PCC subspaces not used in reduced HW systems.
>>>> + * @header: Pointer to the ACPI subtable header under the PCCT.
>>>> + * @end: End of subtable entry.
>>>> + *
>>>> + * Return: If we find a PCC subspace entry that is one of the types used
>>>> + * in reduced hardware systems, return -EINVAL. Otherwise, return 0.
>>>> + *
>>>> + * This gets called for each subtable in the PCC table.
>>>> + */
>>>> +static int count_pcc_subspaces(struct acpi_subtable_header *header,
>>>> + const unsigned long end)
>>>> +{
>>>> + struct acpi_pcct_subspace *pcct_ss = (struct acpi_pcct_subspace *) header;
>>>> +
>>>> + if ((pcct_ss->header.type <= ACPI_PCCT_TYPE_RESERVED) &&
>>>> + (pcct_ss->header.type != ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE) &&
>>>> + (pcct_ss->header.type != ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2))
>>>> + return 0;
>>>> +
>>>> + return -EINVAL;
>>>> +}
>>>> +
>>>> /**
>>>> - * parse_pcc_subspace - Parse the PCC table and verify PCC subspace
>>>> - * entries. There should be one entry per PCC client.
>>>> + * parse_pcc_subspaces -- Count PCC subspaces used only in reduced HW systems.
>>>> * @header: Pointer to the ACPI subtable header under the PCCT.
>>>> * @end: End of subtable entry.
>>>> *
>>>> - * Return: 0 for Success, else errno.
>>>> + * Return: If we find a PCC subspace entry that is one of the types used
>>>> + * in reduced hardware systems, return 0. Otherwise, return -EINVAL.
>>>> *
>>>> * This gets called for each entry in the PCC table.
>>>> */
>>>> @@ -393,10 +417,8 @@ static int parse_pcc_subspace(struct acpi_subtable_header *header,
>>>> if ((pcct_ss->header.type !=
>>>> ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE)
>>>> && (pcct_ss->header.type !=
>>>> - ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2)) {
>>>> - pr_err("Incorrect PCC Subspace type detected\n");
>>>> + ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE_TYPE2))
>>>> return -EINVAL;
>>>> - }
>>>> }
>>>>
>>>> return 0;
>>> Can't we combine parse_pcc_subspace and count_pcc_subspaces into a
>>> single function? parse_pcc_subspace can return 0 for supported subspace
>>> types and -EINVAL for others.
>>
>> I did think about that. The issue is that we have subspaces that are only
>> valid in reduced hardware systems, and subspaces that are not. It might make
>> sense to use different names, as in 'count_reduced_hw_subspaces()' and
>> 'count_general_subspaces()' (or something like those) but we do have the two
>> separate classes and hardware belonging to each of those classes.
>>
>> That being said, you raise a good point: this would only be useful if the
>> mailbox code needed to know the classes of subspaces were different; I saw
>> no such code but I could have missed it. If you're aware of any such cases,
>> let me know. Otherwise, I'll combine the two counting routines and test it.
>>
>>> The limitation on number of subspaces(max = 256) applies to all types of PCC
>>> subspaces (see Table 14-351 in ACPI 6.2). The MAX_PCC_SUBSPACES check in
>>> parse_pcc_subspace seems invalid as pcc_mbox_ctrl.num_chans will not be
>>> initialized yet at that moment.
>>
>> Good catch. Thanks. That test was there prior to my patches, but I'll pull
>> it out.
>>
>>> Given above, I think it is probably better to update parse_pcc_subspace to
>>> only check for a valid PCC subspace type. The check to make sure overall count
>>> of subspace is less than 256 is already present following the call to
>>> acpi_table_parse_entries_array().
>>>
>>> --
>>> Thanks,
>>> Prashanth
>>>
>>
>> Thanks, Prashanth.
>>
>> Rafael: do you want me to just re-send this patch or the whole series? Either
>> way works for me; what's easiest for you since the first two have been applied?
>
> Just this patch, please.
>
> I've applied the other two already.
>
> Thanks,
> Rafael
>

An FYI: I tested v4 of this patch with and without patch 2/3 of this
set (which has already been withdrawn); both cases removed the mostly
incorrect error message.

--
ciao,
al
-----------------------------------
Al Stone
Software Engineer
Red Hat, Inc.
ahs3@redhat.com
-----------------------------------

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