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

[Aleksey Makarov <aleksey.makarov@linaro.org>]

On 03/03/2016 08:48 PM, Peter Hurley wrote:
> 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 <aleksey.makarov@linaro.org>
>>>> ---
>>>>  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.

Is 'setup_fn' ok?

> 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.

Actually it was Mark Salter who asked to introduce such macros.

https://lkml.kernel.org/g/1441730339.5459.8.camel@redhat.com

I think reusing the OF functions is a good decision.

Your "but without any of the real underpinning or flexibility" is unfounded.

> 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);
> }

- Note that this decision forces setting earlycon on GDB2 debug port.
  DBG2 does not specify that it should be exactly earlycon.

- You missed ACPI_DBG2_ARM_DCC.  And actually I think the list of 
  debug ports is open. You will have to make up names like "uart" "pl011"
  each time a new port is introduced into the specs.

- Most important thing, this way you disclose the internals of serial ports
  to the generic earlycon.c  Such info as access mode should stay 
  in the respective drivers.

- I would not like printing address and then parsing it back.

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

To support earlycon on other types of debug port just add literally one
string of code (as in pl011).

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