Subject: [PATCH v3 5/7] ACPI: serial: implement earlycon on ACPI DBG2 port

From: [email-masked] (Peter Hurley)
Date: Thu, 3 Mar 2016 09:48:04 -0800

On 03/01/2016 08:57 AM, Aleksey Makarov wrote:
> 
> 
> On 03/01/2016 06:53 PM, Peter Hurley wrote:
>> On 02/29/2016 04:42 AM, Aleksey Makarov wrote:
>>> Add ACPI_DBG2_EARLYCON_DECLARE() macros that declares
>>> an earlycon on the serial port specified in the DBG2 ACPI table.
>>>
>>> Pass the string "earlycon=acpi_dbg2" to the kernel to activate it.
>>>
>>> Callbacks for EARLYCON_DECLARE() and OF_EARLYCON_DECLARE()
>>> can also be used for this macros.
>>>
>>> Signed-off-by: Aleksey Makarov <[email-masked]>
>>> ---
>>>  Documentation/kernel-parameters.txt |  3 ++
>>>  drivers/tty/serial/earlycon.c       | 60 +++++++++++++++++++++++++++++++++++++
>>>  include/linux/acpi_dbg2.h           | 20 +++++++++++++
>>>  3 files changed, 83 insertions(+)
>>>
>>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>>> index e0a21e4..19b947b 100644
>>> --- a/Documentation/kernel-parameters.txt
>>> +++ b/Documentation/kernel-parameters.txt
>>> @@ -1072,6 +1072,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>>  			A valid base address must be provided, and the serial
>>>  			port must already be setup and configured.
>>>  
>>> +		acpi_dbg2
>>> +			Use serial port specified by the DBG2 ACPI table.
>>> +
>>>  	earlyprintk=	[X86,SH,BLACKFIN,ARM,M68k]
>>>  			earlyprintk=vga
>>>  			earlyprintk=efi
>>> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
>>> index d217366..9ba3a04 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>
>>> @@ -200,6 +201,8 @@ int __init setup_earlycon(char *buf)
>>>  	return -ENOENT;
>>>  }
>>>  
>>> +static bool setup_dbg2_earlycon;
>>> +
>>>  /* early_param wrapper for setup_earlycon() */
>>>  static int __init param_setup_earlycon(char *buf)
>>>  {
>>> @@ -212,6 +215,11 @@ static int __init param_setup_earlycon(char *buf)
>>>  	if (!buf || !buf[0])
>>>  		return early_init_dt_scan_chosen_serial();
>>>  
>>> +	if (!strcmp(buf, "acpi_dbg2")) {
>>> +		setup_dbg2_earlycon = true;
>>> +		return 0;
>>> +	}
>>
>> So this series doesn't start an ACPI earlycon at early_param time?
>> That doesn't seem very useful.
>>
>> When does the ACPI earlycon actually start?
>> And don't say "when the DBG2 table is probed"; that much is obvious.
> 
> ACPI earlycon starts as soon as ACPI tables become accessible (setup_arch()).
> I think that is still quite early.

I see now; the probe is in patch 6/7.

setup_arch()
  acpi_boot_table_init()
    acpi_probe_device_table()
      ...
        acpi_dbg2_setup()
          ->setup()
            acpi_setup_earlycon()

>>> +
>>>  	err = setup_earlycon(buf);
>>>  	if (err == -ENOENT || err == -EALREADY)
>>>  		return 0;
>>> @@ -286,3 +294,55 @@ int __init of_setup_earlycon(const struct earlycon_id *match,
>>>  }
>>>  
>>>  #endif /* CONFIG_OF_EARLY_FLATTREE */
>>> +
>>> +#ifdef CONFIG_ACPI_DBG2_TABLE
>>> +
>>> +int __init acpi_setup_earlycon(struct acpi_dbg2_device *device, void *d)
>>> +{
>>> +	int err;
>>> +	struct uart_port *port = &early_console_dev.port;
>>> +	int (*setup)(struct earlycon_device *, const char *) = d;
>>> +	struct acpi_generic_address *reg;
>>> +
>>> +	if (!setup_dbg2_earlycon)
>>> +		return -ENODEV;
>>> +
>>> +	if (device->register_count < 1)
>>> +		return -ENODEV;
>>> +
>>> +	if (device->base_address_offset >= device->length)
>>> +		return -EINVAL;
>>> +
>>> +	reg = (void *)device + device->base_address_offset;
>>> +
>>> +	if (reg->space_id != ACPI_ADR_SPACE_SYSTEM_MEMORY &&
>>> +	    reg->space_id != ACPI_ADR_SPACE_SYSTEM_IO)
>>> +		return -EINVAL;
>>> +
>>> +	spin_lock_init(&port->lock);
>>> +	port->uartclk = BASE_BAUD * 16;
>>> +
>>> +	if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) {
>>> +		if (device->port_type == ACPI_DBG2_ARM_SBSA_32BIT)
>>> +			port->iotype = UPIO_MEM32;
>>> +		else
>>> +			port->iotype = UPIO_MEM;
>>> +		port->mapbase = reg->address;
>>> +		port->membase = earlycon_map(reg->address, SZ_4K);
>>> +	} else {
>>> +		port->iotype = UPIO_PORT;
>>> +		port->iobase = reg->address;
>>> +	}
>>> +
>>> +	early_console_dev.con->data = &early_console_dev;
>>> +	err = setup(&early_console_dev, NULL);
>>> +	if (err < 0)
>>> +		return err;
>>> +	if (!early_console_dev.con->write)
>>> +		return -ENODEV;
>>> +
>>> +	register_console(early_console_dev.con);
>>> +	return 0;
>>> +}
>>> +
>>> +#endif /* CONFIG_ACPI_DBG2_TABLE */
>>> diff --git a/include/linux/acpi_dbg2.h b/include/linux/acpi_dbg2.h
>>> index 125ae7e..b653752 100644
>>> --- a/include/linux/acpi_dbg2.h
>>> +++ b/include/linux/acpi_dbg2.h
>>> @@ -37,12 +37,32 @@ int acpi_dbg2_setup(struct acpi_table_header *header, const void *data);
>>>  	ACPI_DECLARE_PROBE_ENTRY(dbg2, name, ACPI_SIG_DBG2,		\
>>>  				 acpi_dbg2_setup, &__acpi_dbg2_data_##name)
>>>  
>>> +int acpi_setup_earlycon(struct acpi_dbg2_device *device, void *d);
>>> +
>>> +/**
>>> + * ACPI_DBG2_EARLYCON_DECLARE() - Define handler for ACPI GDB2 serial port
>>> + * @name:		Identifier to compose name of table data
>>> + * @subtype:		Subtype of the port
>>> + * @console_setup:	Function to be called to setup the port
>>> + *
>>> + * Type of the console_setup() callback is
>>> + * int (*setup)(struct earlycon_device *, const char *)
>>> + * It's the type of callback of of_setup_earlycon().
>>> + */
>>> +#define ACPI_DBG2_EARLYCON_DECLARE(name, subtype, console_setup)	\
>>> +	ACPI_DBG2_DECLARE(name, ACPI_DBG2_SERIAL_PORT, subtype,		\
>>> +			  acpi_setup_earlycon, console_setup)
>>> +
>>>  #else
>>>  
>>>  #define ACPI_DBG2_DECLARE(name, type, subtype, setup_fn, data_ptr)	\
>>>  	static const void *__acpi_dbg_data_##name[]			\
>>>  		__used __initdata = { (void *)setup_fn,	(void *)data_ptr }
>>>  
>>> +#define ACPI_DBG2_EARLYCON_DECLARE(name, subtype, console_setup)	\
>>> +	static const void *__acpi_dbg_data_serial_##name[]		\
>>> +		__used __initdata = { (void *)console_setup }

console_setup is a terrible macro argument name; console_setup() is an
actual kernel function (although file-scope).
Please change it to something short and generic.

Honestly, I'd just prefer you skip all this apparatus that makes
ACPI earlycon appear to be like OF earlycon code-wise, but without any of
the real underpinning or flexibility.

This would be trivial to parse the ACPI table and invoke
setup_earlycon() with a string specifier instead.

For example,

int __init acpi_earlycon_setup(struct acpi_dbg2_device *dbg2)
{
        char opts[64];
        struct acpi_generic_addr *addr = (void*)dbg2 + dbg2->base_address_offset;
	int mmio = addr->space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY;

        if (dbg2->port_type != ACPI_DBG2_SERIAL_PORT)
                return 0;

        switch (dbg2->port_subtype) {
        case ACPI_DBG2_ARM_PL011:
	case ACPI_DBG2_ARM_SBSA_GENERIC:
	case ACPI_DBG2_BCM2835:
                sprintf(opts, "pl011,%s,0x%llx", mmio, addr->address);
                break;
        case ACPI_DBG2_ARM_SBSA_32BIT:
                sprintf(opts, "pl011,mmio32,0x%llx", addr->address);
                break;
        case ACPI_DBG2_16550_COMPATIBLE:
        case ACPI_DBG2_16550_SUBSET:
                sprintf(opts, "uart,%s,0x%llx", mmio, addr->address);
                break;
        default:
                return 0;
        }

	return setup_earlycon(opts);
}

This supports every earlycon ACPI DBG2 declares, not just the ARM_PL011
subtype of your series.

>>> +
>>>  #endif
>>>  #endif