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SubjectRe: [PATCH v6 3/5] ACPI: parse SPCR and enable matching console
Date
On Thursday, March 24, 2016 03:52:01 PM Aleksey Makarov wrote:
> 'ARM Server Base Boot Requiremets' [1] mentions SPCR (Serial Port
> Console Redirection Table) [2] as a mandatory ACPI table that
> specifies the configuration of serial console.
>
> Defer initialization of DT earlycon until ACPI/DT decision is made.
>
> If ACPI is enabled, parse the table, setup earlycon
> and enable the specified console.
>
> If it is disabled, try to set up earlycon from DT.
>
> Thanks to Peter Hurley for explaining how this should work.
>
> [1] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0044a/index.html
> [2] https://msdn.microsoft.com/en-us/library/windows/hardware/dn639132(v=vs.85).aspx
>
> Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
> ---
> drivers/acpi/Kconfig | 3 +
> drivers/acpi/Makefile | 1 +
> drivers/acpi/spcr.c | 125 ++++++++++++++++++++++++++++++++++++++++++
> drivers/tty/serial/earlycon.c | 11 +++-
> include/linux/acpi.h | 8 +++
> 5 files changed, 146 insertions(+), 2 deletions(-)
> create mode 100644 drivers/acpi/spcr.c
>
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index 65fb483..5611eb6 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -77,6 +77,9 @@ config ACPI_DEBUGGER_USER
>
> endif
>
> +config ACPI_SPCR_TABLE
> + bool
> +
> config ACPI_SLEEP
> bool
> depends on SUSPEND || HIBERNATION
> diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
> index 7395928..f70ae14 100644
> --- a/drivers/acpi/Makefile
> +++ b/drivers/acpi/Makefile
> @@ -82,6 +82,7 @@ obj-$(CONFIG_ACPI_EC_DEBUGFS) += ec_sys.o
> obj-$(CONFIG_ACPI_CUSTOM_METHOD)+= custom_method.o
> obj-$(CONFIG_ACPI_BGRT) += bgrt.o
> obj-$(CONFIG_ACPI_CPPC_LIB) += cppc_acpi.o
> +obj-$(CONFIG_ACPI_SPCR_TABLE) += spcr.o
> obj-$(CONFIG_ACPI_DEBUGGER_USER) += acpi_dbg.o
>
> # processor has its own "processor." module_param namespace
> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> new file mode 100644
> index 0000000..31e667e
> --- /dev/null
> +++ b/drivers/acpi/spcr.c
> @@ -0,0 +1,125 @@
> +/*
> + * Copyright (c) 2012, Intel Corporation
> + * Copyright (c) 2015, Red Hat, Inc.
> + * Copyright (c) 2015, 2016 Linaro Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + */
> +
> +#define pr_fmt(fmt) "ACPI: SPCR: " fmt
> +
> +#include <linux/acpi.h>
> +#include <linux/console.h>
> +#include <linux/kernel.h>
> +#include <linux/serial_core.h>
> +#include <linux/of_fdt.h>
> +
> +static bool earlycon_init_is_deferred __initdata;
> +
> +void __init defer_earlycon_init(void)
> +{
> + earlycon_init_is_deferred = true;
> +}
> +
> +/**
> + * parse_spcr() - parse ACPI SPCR table and add preferred console
> + *
> + * For the architectures with support for ACPI, CONFIG_ACPI_SPCR_TABLE may be
> + * defined to parse ACPI SPCR table. As a result of the parsing preferred
> + * console is registered.
> + *
> + * When CONFIG_ACPI_SPCR_TABLE is defined, this function should should be called
> + * from arch inintialization code as soon as the DT/ACPI decision is made.
> + *
> + * When CONFIG_ACPI_SPCR_TABLE is defined, "earlycon" without parameters in
> + * command line does not start DT earlycon immediately, instead it defers
> + * starting it until DT/ACPI decision is made. If ACPI is enabled at that time,
> + * parse_spcr() parses the table, adds preferred console and sets up it as an
> + * earlycon. If ACPI is disabled at that time, it tries to set up earlycon
> + * from DT.
> + */
> +int __init parse_spcr(void)
> +{
> +#define OPTS_LEN 64

I'm not sure if you need that symbol.

ISTR that sizeof(opts) will give you the size of the array (but maybe I'm
confusing this with something else).

> + static char opts[OPTS_LEN];
> + struct acpi_table_spcr *table;
> + acpi_size table_size;
> + acpi_status status;
> + char *uart;
> + char *iotype;
> + int baud_rate;
> + int err;
> +
> + if (acpi_disabled)
> + return earlycon_init_is_deferred ?
> + early_init_dt_scan_chosen_stdout() : 0;

I would prefer this to be arranged differently, so a specific error value is
returned when ACPI is disabled and the the fallback to DT happens in the
caller (if it cares about DT, that is).

> +
> + status = acpi_get_table_with_size(ACPI_SIG_SPCR, 0,
> + (struct acpi_table_header **)&table,
> + &table_size);
> +
> + if (ACPI_FAILURE(status))
> + return -ENOENT;
> +
> + if (table->header.revision < 2) {
> + err = -EINVAL;

Why -EINVAL?

> + pr_err("wrong table version\n");
> + goto done;
> + }
> +
> + iotype = (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) ?

The parens are not necessary.

Thanks,
Rafael

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