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

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Message-ID: <CAOZdJXV4E6gu=Ed6nOCcEp2afe_g8Ot-H5oO5=6+ye51cv9hUg@mail.gmail.com>
Date:   Thu, 7 Dec 2017 12:43:26 -0600
From:   Timur Tabi <timur@...eaurora.org>
To:     Prarit Bhargava <prarit@...hat.com>
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 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.

> +
> +/*
> + * 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().

> +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.

-- 
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Code Aurora Forum, a Linux Foundation Collaborative Project.