Subject: [PATCH v5 3/6] ACPI: parse SPCR and enable matching console

From: [email-masked] (Peter Hurley)
Date: Tue, 22 Mar 2016 07:57:04 -0700

On 03/22/2016 05:26 AM, Yury Norov wrote:
> On Tue, Mar 22, 2016 at 01:46:30PM +0300, 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, setup earlycon and enable the specified console.
>>
>> 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 <[email-masked]>
>> ---
>>  drivers/acpi/Kconfig          |   3 ++
>>  drivers/acpi/Makefile         |   1 +
>>  drivers/acpi/spcr.c           | 102 ++++++++++++++++++++++++++++++++++++++++++
>>  drivers/tty/serial/earlycon.c |  13 ++++--
>>  include/linux/acpi.h          |   8 ++++
>>  5 files changed, 123 insertions(+), 4 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..1ec82f9
>> --- /dev/null
>> +++ b/drivers/acpi/spcr.c
>> @@ -0,0 +1,102 @@
>> +/*
>> + * 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 bool init_earlycon;
>> +
>> +void __init init_spcr_earlycon(void)
>> +{
>> +	init_earlycon = true;
>> +}
>> +
> 
> 1. I see you keep in mind multiple access.

Concurrent access is not a concern here: only the boot cpu is running
and intrs are off.

The "init_earlycon" flag is used because parsing the "earlycon" early param
is earlier than parsing ACPI tables.

 Then you'd worry about race
> conditions as well. In this case, I'd consider atomic access to
> variable.
> 2. It seems you need is_init() helper too.
> 
>> +int __init parse_spcr(void)
>> +{
>> +	static char opts[64];
>> +	struct acpi_table_spcr *table;
>> +	acpi_size table_size;
>> +	acpi_status status;
>> +	char *uart;
>> +	char *iotype;
>> +	int baud_rate;
>> +	int err = 0;
> 
> You can do not initialize 'err'.

Why?

> 
>> +
>> +	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;
>> +		pr_err("wrong table version\n");
>> +		goto done;
>> +	}
>> +
>> +	iotype = (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) ?
>> +			"mmio" : "io";
>> +
>> +	switch (table->interface_type) {
>> +	case ACPI_DBG2_ARM_SBSA_32BIT:
>> +		iotype = "mmio32";
>> +		/* fall through */
>> +	case ACPI_DBG2_ARM_PL011:
>> +	case ACPI_DBG2_ARM_SBSA_GENERIC:
>> +	case ACPI_DBG2_BCM2835:
>> +		uart = "pl011";
>> +		break;
>> +	case ACPI_DBG2_16550_COMPATIBLE:
>> +	case ACPI_DBG2_16550_SUBSET:
>> +		uart = "uart";
>> +		break;
>> +	default:
>> +		err = -ENOENT;
>> +		goto done;
>> +	}
>> +
>> +	switch (table->baud_rate) {
>> +	case 3:
>> +		baud_rate = 9600;
>> +		break;
>> +	case 4:
>> +		baud_rate = 19200;
>> +		break;
>> +	case 6:
>> +		baud_rate = 57600;
>> +		break;
>> +	case 7:
>> +		baud_rate = 115200;
>> +		break;
>> +	default:
>> +		err = -ENOENT;
>> +		goto done;
>> +	}
>> +
>> +	sprintf(opts, "%s,%s,0x%llx,%d", uart, iotype,
>> +		table->serial_port.address, baud_rate);
> 
> As 'opts' is static, don't you need to take some measures to prevent
> concurrent access. The simpler measure for me is to declare it on
> stack.

Again, concurrent access is not a concern at this early time.

Regards,
Peter Hurley

>> +
>> +	pr_info("console: %s", opts);
>> +
>> +	if (init_earlycon)
>> +		setup_earlycon(opts);
>> +
>> +	err = add_preferred_console(uart, 0, opts + strlen(uart) + 1);
>> +
>> +done:
>> +	early_acpi_os_unmap_memory((void __iomem *)table, table_size);
>> +	return err;
>> +}
>> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
>> index d217366..ec030c9 100644
>> --- a/drivers/tty/serial/earlycon.c
>> +++ b/drivers/tty/serial/earlycon.c
>> @@ -22,6 +22,7 @@
>>  #include <linux/sizes.h>
>>  #include <linux/of.h>
>>  #include <linux/of_fdt.h>
>> +#include <linux/acpi.h>
>>  
>>  #ifdef CONFIG_FIX_EARLYCON_MEM
>>  #include <asm/fixmap.h>
>> @@ -206,11 +207,15 @@ static int __init param_setup_earlycon(char *buf)
>>  	int err;
>>  
>>  	/*
>> -	 * Just 'earlycon' is a valid param for devicetree earlycons;
>> -	 * don't generate a warning from parse_early_params() in that case
>> +	 * Just 'earlycon' is a valid param for devicetree and ACPI SPCR
>> +	 * earlycons; don't generate a warning from parse_early_params()
>> +	 * in that case
>>  	 */
>> -	if (!buf || !buf[0])
>> -		return early_init_dt_scan_chosen_serial();
>> +	if (!buf || !buf[0]) {
>> +		init_spcr_earlycon();
>> +		early_init_dt_scan_chosen_serial();
>> +		return 0;
>> +	}
>>  
>>  	err = setup_earlycon(buf);
>>  	if (err == -ENOENT || err == -EALREADY)
>> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
>> index 06ed7e5..ebbb212 100644
>> --- a/include/linux/acpi.h
>> +++ b/include/linux/acpi.h
>> @@ -1004,4 +1004,12 @@ static inline struct fwnode_handle *acpi_get_next_subnode(struct device *dev,
>>  #define acpi_probe_device_table(t)	({ int __r = 0; __r;})
>>  #endif
>>  
>> +#ifdef CONFIG_ACPI_SPCR_TABLE
>> +int parse_spcr(void);
>> +void init_spcr_earlycon(void);
>> +#else
>> +static inline  int parse_spcr(void) { return 0; }
>> +static inline void init_spcr_earlycon(void) {}
>> +#endif
>> +
>>  #endif	/*_LINUX_ACPI_H*/
>> -- 
>> 2.7.4