linux-kernel - Re: [PATCH 1/2] acpi, spcr: Make SPCR avialable to other architectures

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Date:   Thu, 7 Dec 2017 14:05:20 -0500
From:   Prarit Bhargava <prarit@...hat.com>
To:     Timur Tabi <timur@...eaurora.org>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-pm@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        linux-doc@...r.kernel.org, Will Deacon <will.deacon@....com>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Lv Zheng <lv.zheng@...el.com>, linux-serial@...r.kernel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>
Subject: Re: [PATCH 1/2] acpi, spcr: Make SPCR avialable to other
 architectures



On 12/07/2017 01:43 PM, Timur Tabi wrote:
> On Thu, Dec 7, 2017 at 11:29 AM, Prarit Bhargava <prarit@...hat.com> wrote:
>> Other architectures can use SPCR to setup an early console or console but
>> the current code is ARM64 specific.
>>
>> Change the name of parse_spcr() to acpi_parse_spcr().  Add a weak
>> function acpi_arch_setup_console() that can be used for arch-specific
>> setup.  Move SPCR initialization flag into ACPI code.  Update the
>> Documention on the use of the SPCR earlycon.
>>
>> This patch does not change arm64 behaviour.
> 
> Let's hope so.  Our E44 erratum work-around has caused lots of
> problems in the past, so the code is a bit fragile.
> 
>> +static bool qdf2400_erratum_44_present(struct acpi_table_header *h)
>> +{
>> +       if (memcmp(h->oem_id, "QCOM  ", ACPI_OEM_ID_SIZE))
>> +               return false;
>> +
>> +       if (!memcmp(h->oem_table_id, "QDF2432 ", ACPI_OEM_TABLE_ID_SIZE))
>> +               return true;
>> +
>> +       if (!memcmp(h->oem_table_id, "QDF2400 ", ACPI_OEM_TABLE_ID_SIZE) &&
>> +                       h->oem_revision == 1)
>> +               return true;
>> +
>> +       return false;
>> +}
> 
> Please give us a chance to test this patch before merging. We've had a
> lot of problems with our E44 work-around, and we need to make sure
> that qdf2400_erratum_44_present function is called before the pl011
> driver is probed.

Timor, do you know of a specific system that has this problem?  If so, I
could see if we have one @ Red Hat and test on it to verify the WAR.

> 
>> +
>> +/*
>> + * APM X-Gene v1 and v2 UART hardware is an 16550 like device but has its
>> + * register aligned to 32-bit. In addition, the BIOS also encoded the
>> + * access width to be 8 bits. This function detects this errata condition.
>> + */
>> +static bool xgene_8250_erratum_present(struct acpi_table_spcr *tb)
>> +{
>> +       bool xgene_8250 = false;
>> +
>> +       if (tb->interface_type != ACPI_DBG2_16550_COMPATIBLE)
>> +               return false;
>> +
>> +       if (memcmp(tb->header.oem_id, "APMC0D", ACPI_OEM_ID_SIZE) &&
>> +           memcmp(tb->header.oem_id, "HPE   ", ACPI_OEM_ID_SIZE))
>> +               return false;
>> +
>> +       if (!memcmp(tb->header.oem_table_id, "XGENESPC",
>> +           ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 0)
>> +               xgene_8250 = true;
>> +
>> +       if (!memcmp(tb->header.oem_table_id, "ProLiant",
>> +           ACPI_OEM_TABLE_ID_SIZE) && tb->header.oem_revision == 1)
>> +               xgene_8250 = true;
>> +
>> +       return xgene_8250;
>> +}
> 
> I suspect that this function has the same issues as
> qdf2400_erratum_44_present().
>

Ditto.

>> +config ACPI_SPCR_TABLE
>> +       bool "ACPI Serial Port Console Redirection Support"
>> +       default y if ARM64
>> +       help
>> +         Enable support for Serial Port Console Redirection (SPCR) Table.
>> +         This table provides information about the configuration of the
>> +         earlycon console.
>> +
> 
> So ACPI without SPCR has never been tested by us.  Making it optional
> makes me a little nervous.  We'll have to evaluate this change.
> 

It is 'y' for ARM64?  Maybe I have that wrong but I thought that would
always build it for ARM64.

P.