Re: [PATCH] ACPI: SPCR: Use access width to determine mmio usage

[Loc Ho]

Hi Jon,

>>> >> >>>>>> The current SPCR code does not check the access width of the mmio, and
>>> >> >>>>>> uses a default of 8bit register accesses.  This prevents devices that
>>> >> >>>>>> only do 16 or 32bit register accesses from working.  By simply checking
>>> >> >>>>>> this field and setting the mmio string appropriately, this issue can be
>>> >> >>>>>> corrected.  To prevent any legacy issues, the code will default to 8bit
>>> >> >>>>>> accesses if the value is anything but 16 or 32.
>>> >> >>>>>
>>> >> >>>>> Thanks for this. Just as an FYI I've a running discussion with Microsoft
>>> >> >>>>> about defining additional UART subtypes in the DBG2 for special case
>>> >> >>>>> UARTs. Specifically, I want to address AppliedMicro's special 8250 dw IP
>>> >> >>>>> that also has a non-standard clock. At this time, there is general
>>> >> >>>>> agreement to use the access width for some cases rather than defining
>>> >> >>>>> yet more subtypes - so your patch is good.
>>> >> >>>>>
>>> >> >>>>> Loc/Applied: please track this thread, incorporate feedback, and also
>>> >> >>>>> track the other general recent discussions of 8250 dw from this week.
>>> >> >>>>
>>> >> >>>> Thanks for forward me this patch. This patch does not work with X-Gene
>>> >> >>>> v1 and v2 SoC's. As BIOS SPCR encodes these info as:
>>> >> >>>>
>>> >> >>>> Bit Width: 32
>>> >> >>>> Bit Offset: 0
>>> >> >>>> Encoded Access Width: 01 (Byte Access)
>>> >> >>>>
>>> >> >>>> With this patch, it would use the "mmio" instead the "mmio32" as with
>>> >> >>>> this patch - https://patchwork.kernel.org/patch/9460959
>>> >> >>>
>>> >> >>> I think this is why we need the DBG2 subtype for Applied X-Gene1. I'm
>>> >> >>> hoping the update to the SPCR/DBG2 spec is done soon.
>>> >> >>
>>> >> >> We can't rely on the BIOS change to support this new subtype as we
>>> >> >> have system that is already in production deployment. When these
>>> >> >> system upgrade to new version of the OS (stock, RHELSA, or whatever),
>>> >> >> they will break. We need the patch from
>>> >> >> https://patchwork.kernel.org/patch/9460959/ rolled upstream.
>>> >> >
>>> >> > There is no reason why the patch you reference cannot co-exist with
>>> >> > the one I am submitting here.  In this case, my patch would set it to
>>> >> > mmio, then the patch you link above would reset it to mmio32.
>>> >> > Personally, I would recommend a big, fat comment on why this extra
>>> >> > step is necessary, but it should work as desired.  Alternatively, we
>>> >> > could add some kind of quirk library (similar to
>>> >> > qdf2400_erratum_44_present) where the OEM/OEM Table ID is referenced
>>> >> > and workaround applied.  Thoughts?
>>> >>
>>> >> That's was my first version but after seeing both versions, I think
>>> >> they are better solution as it works for more SoC's than just our. As
>>> >> you had suggested, we should apply your patch and
>>> >> https://patchwork.kernel.org/patch/9460959. The third patch -
>>> >> https://patchwork.kernel.org/patch/9462183/ - conflicts with your.
>>> >>
>>> >> Summary:
>>> >> 1. Applied your - https://lkml.org/lkml/2017/5/4/450
>>> >> 2. Applied this one - https://patchwork.kernel.org/patch/9460959/
>>> >>
>>> >> -Loc
>>> >
>>> > What if we simply applied the following (100% untested) patch to add
>>> > the quirk framework I was suggesting?  It can be applied on top of the
>>> > patch I submitted previously.
>>>
>>> It is a bit more complex that this simple patch. How about this one
>>> (my original version). As for Jon Master question on McDivitt, not
>>> sure what they use for the ACPI table for SPCR. If they used our
>>> reference, then this might work for them too. This version would limit
>>> to just the existent firmware or until the SPCR table gets changed.
>>>
>>>
>>> tty: 8250: Workaround for APM X-Gene 8250 UART 32-alignment errata
>>>
>>> APM X-Gene verion 1 and 2 have an 8250 UART with its register
>>> aligned to 32-bit. The SPCR always assumes fully compatible
>>> 8250. This causes no console with ACPI boot as the console
>>> will not match X-Gene UART port due to the lack of mmio32
>>> option.
>>>
>>> Signed-off-by: Loc Ho <lho@xxxxxxx>
>>> ---
>>>  drivers/acpi/spcr.c | 21 +++++++++++++++++++++
>>>  1 file changed, 21 insertions(+)
>>>
>>> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
>>> index 3afa8c1..77b45a0 100644
>>> --- a/drivers/acpi/spcr.c
>>> +++ b/drivers/acpi/spcr.c
>>> @@ -36,6 +36,25 @@ static bool qdf2400_erratum_44_present(struct
>>> acpi_table_header *h)
>>>         return false;
>>>  }
>>>
>>> +/*
>>> + * APM X-Gene v1 and v2 UART hardware is an 16550 like device but has its
>>> + * register aligned to 32-bit. This function detects this errata condition.
>>> + */
>>> +static bool xgene_8250_erratum_present(struct acpi_table_spcr *tb)
>>> +{
>>> +       if (tb->interface_type != ACPI_DBG2_16550_COMPATIBLE)
>>> +               return false;
>>> +
>>> +       if (memcmp(tb->header.oem_id, "APMC0D", ACPI_OEM_ID_SIZE))
>>> +               return false;
>>> +
>>> +       if (!memcmp(tb->header.oem_table_id, "XGENESPC",
>>> +                   ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 0)
>>> +               return true;
>>> +
>>> +       return false;
>>> +}
>>> +
>>>  /**
>>>   * parse_spcr() - parse ACPI SPCR table and add preferred console
>>>   *
>>> @@ -115,6 +134,8 @@ int __init parse_spcr(bool earlycon)
>>>
>>>         if (qdf2400_erratum_44_present(&table->header))
>>>                 uart = "qdf2400_e44";
>>> +       if (xgene_8250_erratum_present(table))
>>> +               iotype = "mmio32";
>>>
>>>         snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
>>>                  table->serial_port.address, baud_rate);
>>>
>>
>> I didn't see a follow up email on this. What was the conclusion to
>> this patch series?
>
> I have not received an ack, nack, or gtfo from any of the maintainers
> of this file.  Per
> ./scripts/get_maintainer.pl drivers/acpi/spcr.c
> "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx> (supporter:ACPI)
> Len Brown <lenb@xxxxxxxxxx> (supporter:ACPI)
> linux-acpi@xxxxxxxxxxxxxxx (open list:ACPI)
> linux-kernel@xxxxxxxxxxxxxxx (open list)
>
> Is there someone else I should be directing this patch through?

Can you generate a new patch set that includes all the required
patches (including mine workaround for X-Gene) and re-post? Then we
check with Rafael or Len again.

-Loc