Re: [Linaro-acpi] [RFC 3/5] acpi/serial: add DBG2 earlycon support

[Leif Lindholm]

On Tue, Sep 08, 2015 at 12:38:59PM -0400, Mark Salter wrote:
> On Tue, 2015-09-08 at 13:43 +0100, Leif Lindholm wrote:
> > The ACPI DBG2 table defines a debug console. Add support for parsing it
> > and using it to select earlycon destination when no arguments provided.
> > 
> > Signed-off-by: Leif Lindholm <leif.lindholm@xxxxxxxxxx>
> > ---
> >  arch/arm64/kernel/acpi.c      |   2 +
> >  drivers/acpi/Makefile         |   1 +
> >  drivers/acpi/console.c        | 103 ++++++++++++++++++++++++++++++++++++++++++
> >  drivers/of/fdt.c              |   2 +-
> >  drivers/tty/serial/earlycon.c |  16 ++++---
> >  include/linux/acpi.h          |   4 ++
> >  include/linux/serial_core.h   |   9 ++--
> >  7 files changed, 126 insertions(+), 11 deletions(-)
> >  create mode 100644 drivers/acpi/console.c
> > 
> > diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> > index b9a5623..be7600a 100644
> > --- a/arch/arm64/kernel/acpi.c
> > +++ b/arch/arm64/kernel/acpi.c
> > @@ -207,6 +207,8 @@ void __init acpi_boot_table_init(void)
> >  		if (!param_acpi_force)
> >  			disable_acpi();
> >  	}
> > +
> > +	acpi_early_console_probe();
> >  }
> >  
> >  void __init acpi_gic_init(void)
> > diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
> > index b5e7cd8..a89587d 100644
> > --- a/drivers/acpi/Makefile
> > +++ b/drivers/acpi/Makefile
> > @@ -10,6 +10,7 @@ ccflags-$(CONFIG_ACPI_DEBUG)	+= -DACPI_DEBUG_OUTPUT
> >  #
> >  obj-y				+= tables.o
> >  obj-$(CONFIG_X86)		+= blacklist.o
> > +obj-y				+= console.o
> 
> obj-$(CONFIG_SERIAL_EARLYCON) += console.o
> 
> to eliminate whole-file #ifdef

Yes, that makes more sense for this patch standalone, but I felt it
would be a bit weird to add the conditionality here only to delete it
in the subsequent patch. I don't feel strongly about it.

> >  
> >  #
> >  # ACPI Core Subsystem (Interpreter)
> > diff --git a/drivers/acpi/console.c b/drivers/acpi/console.c
> > new file mode 100644
> > index 0000000..a985890
> > --- /dev/null
> > +++ b/drivers/acpi/console.c
> > @@ -0,0 +1,103 @@
> > +/*
> > + * Copyright (c) 2012, Intel Corporation
> > + * Copyright (c) 2015, 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 DEBUG
> > +#define pr_fmt(fmt) "ACPI: " KBUILD_MODNAME ": " fmt
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/kernel.h>
> > +#include <linux/serial_core.h>
> > +
> > +#define NUM_ELEMS(x) (sizeof(x) / sizeof(*x))
> > +
> > +#ifdef CONFIG_SERIAL_EARLYCON
> > +static int use_earlycon __initdata;
> > +static int __init setup_acpi_earlycon(char *buf)
> > +{
> > +	if (!buf)
> > +		use_earlycon = 1;
> > +
> > +	return 0;
> > +}
> > +early_param("earlycon", setup_acpi_earlycon);
> > +
> > +extern struct earlycon_id __earlycon_table[];
> > +
> > +static __initdata struct {
> > +	int id;
> > +	const char *name;
> > +} subtypes[] = {
> > +	{0, "uart8250"},
> > +	{1, "uart8250"},
> > +	{2, NULL},
> > +	{3, "pl011"},
> > +};
> 
> Instead of having a table here, why not have an ACPI_EARLYCON_DECLARE()
> where individual drivers can provide an id similar to OF_EARLYCON_DECLARE()
> providing compatible strings?

The IDs are defined by the DBG2 specification, so it felt more
natural to encapsulate it here. However, a comment to that effect
would be useful. Or would you still prefer
ACPI_EARLYCON_DECLARE(0, uart8250)
ACPI_EARLYCON_DECLARE(1, uart8250)
...
?
 
> > +
> > +static int __init acpi_setup_earlycon(unsigned long addr, const char *driver)
> > +{
> > +	const struct earlycon_id *match;
> > +
> > +	for (match = __earlycon_table; match->name[0]; match++)
> > +		if (strcmp(driver, match->name) == 0)
> > +			return setup_earlycon_driver(addr, match->setup);
> > +
> > +	return -ENODEV;
> > +}
> > +
> > +static int __init acpi_parse_dbg2(struct acpi_table_header *table)
> > +{
> > +	struct acpi_table_dbg2 *dbg2;
> > +	struct acpi_dbg2_device *entry;
> > +	void *tbl_end;
> > +
> > +	dbg2 = (struct acpi_table_dbg2 *)table;
> > +	if (!dbg2) {
> > +		pr_debug("DBG2 not present.\n");
> > +		return -ENODEV;
> > +	}
> > +
> > +	tbl_end = (void *)table + table->length;
> > +
> > +	entry = (struct acpi_dbg2_device *)((void *)dbg2 + dbg2->info_offset);
> > +
> > +	while (((void *)entry) + sizeof(struct acpi_dbg2_device) < tbl_end) {
> > +		struct acpi_generic_address *addr;
> > +
> > +		if (entry->revision != 0) {
> > +			pr_debug("DBG2 revision %d not supported.\n",
> > +				 entry->revision);
> > +			return -ENODEV;
> > +		}
> > +
> > +		addr = (void *)entry + entry->base_address_offset;
> > +
> > +		pr_debug("DBG2 PROBE - console (%04x:%04x).\n",
> > +			 entry->port_type, entry->port_subtype);
> > +
> > +		if (use_earlycon &&
> > +		    (entry->port_type == ACPI_DBG2_SERIAL_PORT) &&
> > +		    (entry->port_subtype < NUM_ELEMS(subtypes)))
> > +			acpi_setup_earlycon(addr->address,
> > +					    subtypes[entry->port_subtype].name);
> 
> Don't we need to handle space_id (and bit width) as well as address?

space_id? bit width?
DBG2 is for quite primitive debug ports, already initialised by
formware (or other pre-kernel agent).

> > +
> > +		entry = (struct acpi_dbg2_device *)
> > +			((void *)entry + entry->length);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +int __init acpi_early_console_probe(void)
> > +{
> > +	acpi_table_parse(ACPI_SIG_DBG2, acpi_parse_dbg2);
> > +
> > +	return 0;
> > +}
> > +#endif /* CONFIG_SERIAL_EARLYCON */
> > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > index fcfc4c7..a96209f 100644
> > --- a/drivers/of/fdt.c
> > +++ b/drivers/of/fdt.c
> > @@ -829,7 +829,7 @@ int __init early_init_dt_scan_chosen_serial(void)
> >  		if (!addr)
> >  			return -ENXIO;
> >  
> > -		of_setup_earlycon(addr, match->data);
> > +		setup_earlycon_driver(addr, match->data);
> >  		return 0;
> >  	}
> >  	return -ENODEV;
> > diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> > index 2bda09a..c063cbb 100644
> > --- a/drivers/tty/serial/earlycon.c
> > +++ b/drivers/tty/serial/earlycon.c
> > @@ -13,6 +13,7 @@
> >  
> >  #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
> >  
> > +#include <linux/acpi.h>
> >  #include <linux/console.h>
> >  #include <linux/kernel.h>
> >  #include <linux/init.h>
> > @@ -184,12 +185,16 @@ 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 or ACPI earlycons;
> > +	 * ACPI cannot be parsed yet, so return without action if enabled.
> > +	 * Otherwise, attempt initialization using DT.
> >  	 */
> > -	if (!buf || !buf[0])
> > -		if (IS_ENABLED(CONFIG_OF_FLATTREE))
> > +	if (!buf || !buf[0]) {
> > +		if (!acpi_disabled)
> 
> How do we know for sure that "acpi" has been parsed before "earlycon"?

Because "arch" comes before "drivers" in kernel image link order.
*twitch*
Yes, not the best argument ever.

> > +			return 0;
> > +		else if (IS_ENABLED(CONFIG_OF_FLATTREE))
> >  			return early_init_dt_scan_chosen_serial();
> > +	}
> >  
> >  	err = setup_earlycon(buf);
> >  	if (err == -ENOENT || err == -EALREADY)
> > @@ -198,8 +203,7 @@ static int __init param_setup_earlycon(char *buf)
> >  }
> >  early_param("earlycon", param_setup_earlycon);
> >  
> > -int __init of_setup_earlycon(unsigned long addr,
> > -			     int (*setup)(struct earlycon_device *, const char *))
> > +int __init setup_earlycon_driver(unsigned long addr, earlycon_initfunc_t setup)
> >  {
> >  	int err;
> >  	struct uart_port *port = &early_console_dev.port;
> > diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> > index 7235c48..88cb9c1 100644
> > --- a/include/linux/acpi.h
> > +++ b/include/linux/acpi.h
> > @@ -811,4 +811,8 @@ static inline struct acpi_device *acpi_get_next_child(struct device *dev,
> >  
> >  #endif
> >  
> > +#if defined(CONFIG_ACPI) && defined(CONFIG_SERIAL_EARLYCON)
> > +int __init acpi_early_console_probe(void);
> > +#endif
> > +
> >  #endif	/*_LINUX_ACPI_H*/
> > diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> > index 297d4fa..39e99b0 100644
> > --- a/include/linux/serial_core.h
> > +++ b/include/linux/serial_core.h
> > @@ -339,14 +339,15 @@ struct earlycon_device {
> >  	unsigned int baud;
> >  };
> >  
> > +typedef int (*earlycon_initfunc_t)(struct earlycon_device *, const char *);
> > +
> >  struct earlycon_id {
> > -	char	name[16];
> > -	int	(*setup)(struct earlycon_device *, const char *options);
> > +	char			name[16];
> > +	earlycon_initfunc_t	setup;
> >  } __aligned(32);
> >  
> >  extern int setup_earlycon(char *buf);
> > -extern int of_setup_earlycon(unsigned long addr,
> > -			     int (*setup)(struct earlycon_device *, const char *));
> > +extern int setup_earlycon_driver(unsigned long addr, earlycon_initfunc_t setup);
> >  
> >  #define EARLYCON_DECLARE(_name, func)					\
> >  	static const struct earlycon_id __earlycon_##_name		\
> 
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