Date:   Mon, 3 Jul 2017 11:27:51 -0700
From:   Loc Ho <lho@....com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Jon Mason <jon.mason@...adcom.com>, Jon Masters <jcm@...hat.com>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Lv Zheng <lv.zheng@...el.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "devel@...ica.org" <devel@...ica.org>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
        Aleksey Makarov <aleksey.makarov@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] ACPI: SPCR: Use access width to determine mmio usage

Hi Rafael,

>>>> >> >>>>>> 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@....com>
>>>> ---
>>>>  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@...ysocki.net> (supporter:ACPI)
>> Len Brown <lenb@...nel.org> (supporter:ACPI)
>> linux-acpi@...r.kernel.org (open list:ACPI)
>> linux-kernel@...r.kernel.org (open list)
>>
>> Is there someone else I should be directing this patch through?
>
> Generally, whoever is going to be affected by this change.
>
> git seems to tell me that the spcr.c file went in through the tty tree
> and Aleksey introduced it.
>
> I can apply it if no one has any objections.

I think this is on the mailing list long enough and I don't see anyone
follow up with any objection. Would you applies Jon Mason patch and my
patch on May 8 or inline below? If you need a more formal patch email
for the below patch, I can send one to this email list as well.

==========

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@....com>
---
 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);

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