Message-ID: <56C64366.2070702@hurleysoftware.com>
Date:	Thu, 18 Feb 2016 14:19:18 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Aleksey Makarov <aleksey.makarov@...aro.org>,
	linux-acpi@...r.kernel.org
Cc:	Russell King <linux@....linux.org.uk>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Christopher Covington <cov@...eaurora.org>,
	linux-serial@...r.kernel.org, Jiri Slaby <jslaby@...e.com>,
	Al Stone <ahs3@...hat.com>,
	linux-arm-kernel@...ts.infradead.org, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH v3 2/5] ACPI: parse SPCR and enable matching console

On 02/15/2016 10:05 AM, 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.
> 
> Parse this table and check if any registered console match the
> description.  If it does, enable that console.
> 
> Introduce a new function acpi_console_check().  At the uart port
> registration, this function checks if the ACPI SPCR table specifies
> its argument of type struct uart_port to be a console
> and if so calls add_preferred_console().
> 
> [1] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.den0044a/index.html
> [2] http://msdn.microsoft.com/en-us/library/windows/hardware/dn639131(v=vs.85).aspx
> 
> Signed-off-by: Aleksey Makarov <aleksey.makarov@...aro.org>
> ---
>  drivers/acpi/Kconfig             |  3 ++
>  drivers/acpi/Makefile            |  1 +
>  drivers/acpi/spcr.c              | 97 ++++++++++++++++++++++++++++++++++++++++
>  drivers/tty/serial/serial_core.c | 14 +++++-
>  include/linux/acpi.h             | 10 +++++
>  5 files changed, 123 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 346101c..708b143 100644
> --- a/drivers/acpi/Makefile
> +++ b/drivers/acpi/Makefile
> @@ -81,6 +81,7 @@ 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..a1eca91
> --- /dev/null
> +++ b/drivers/acpi/spcr.c
> @@ -0,0 +1,97 @@
> +/*
> + * 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>
> +
> +static int acpi_table_parse_spcr(int (*handler)(struct acpi_table_spcr *table,
> +						void *data), void *data)
> +{
> +	struct acpi_table_spcr *table = NULL;
> +	acpi_size table_size;
> +	acpi_status status;
> +	int err;
> +
> +	status = acpi_get_table_with_size(ACPI_SIG_SPCR, 0,
> +					  (struct acpi_table_header **)&table,
> +					  &table_size);
> +
> +	if (ACPI_FAILURE(status))
> +		return -ENODEV;
> +
> +	err = handler(table, data);
> +
> +	early_acpi_os_unmap_memory(table, table_size);
> +
> +	return err;
> +}
> +
> +static int spcr_table_handler_check(struct acpi_table_spcr *table, void *data)
> +{
> +	struct uart_port *uport = data;
> +	char *options;
> +
> +	if (table->header.revision < 2)
> +		return -EOPNOTSUPP;
> +
> +	switch (table->baud_rate) {
> +	case 3:
> +		options = "9600";
> +		break;
> +	case 4:
> +		options = "19200";
> +		break;
> +	case 6:
> +		options = "57600";
> +		break;
> +	case 7:
> +		options = "115200";
> +		break;
> +	default:
> +		options = "";
> +		break;
> +	}
> +
> +	if ((table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY &&
> +	     table->serial_port.address == (u64)uport->mapbase) ||
> +	    (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_IO &&
> +	     table->serial_port.address == (u64)uport->iobase)) {
> +		pr_info("adding preferred console [%s%d]\n", uport->cons->name,
> +			uport->line);
> +		add_preferred_console(uport->cons->name, uport->line, options);
> +		return 1;
> +
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * acpi_console_check - Check if uart matches the console specified by SPCR.
> + *
> + * @uport:	uart port to check
> + *
> + * This function checks if the ACPI SPCR table specifies @uport to be a console
> + * and if so calls add_preferred_console()
> + *
> + * Return: a non-error value if the console matches.
> + */
> +bool acpi_console_check(struct uart_port *uport)
> +{
> +	if (acpi_disabled || console_set_on_cmdline)
> +		return false;
> +
> +	return acpi_table_parse_spcr(spcr_table_handler_check, uport) > 0;
> +}
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index a126a60..459ab54 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -34,6 +34,7 @@
>  #include <linux/serial_core.h>
>  #include <linux/delay.h>
>  #include <linux/mutex.h>
> +#include <linux/acpi.h>
>  
>  #include <asm/irq.h>
>  #include <asm/uaccess.h>
> @@ -2654,8 +2655,17 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
>  		spin_lock_init(&uport->lock);
>  		lockdep_set_class(&uport->lock, &port_lock_key);
>  	}
> -	if (uport->cons && uport->dev)
> -		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);
> +
> +	/*
> +	 * Support both open FW and ACPI access to console definitions.
> +	 * Both of_console_check() and acpi_console_check() will call
> +	 * add_preferred_console() if a console definition is found.
> +	 */
> +	if (uport->cons && uport->dev) {
> +		if (!acpi_console_check(uport))
> +			of_console_check(uport->dev->of_node, uport->cons->name,
> +					 uport->line);

of_console_check() is not a good model for enabling a console.
It's a hack with several shortcomings (and bugs) that is tolerated here
because of its broad applicability to a wide range of platforms and drivers.

I specifically added console matching to enable exactly this kind of
console-selection-via-firmware. Please use that facility.

Regards,
Peter Hurley


> +	}
>  
>  	uart_configure_port(drv, state, uport);
>  
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 06ed7e5..ea0c297 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1004,4 +1004,14 @@ static inline struct fwnode_handle *acpi_get_next_subnode(struct device *dev,
>  #define acpi_probe_device_table(t)	({ int __r = 0; __r;})
>  #endif
>  
> +struct uart_port;
> +#ifdef CONFIG_ACPI_SPCR_TABLE
> +bool acpi_console_check(struct uart_port *uport);
> +#else
> +static inline bool acpi_console_check(struct uart_port *uport)
> +{
> +	return FALSE;
> +}
> +#endif
> +
>  #endif	/*_LINUX_ACPI_H*/
> 

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