On Thursday, March 24, 2016 03:52:01 PM 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. > > Defer initialization of DT earlycon until ACPI/DT decision is made. > > If ACPI is enabled, parse the table, setup earlycon > and enable the specified console. > > If it is disabled, try to set up earlycon from DT. > > 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 <aleksey.makarov@xxxxxxxxxx> > --- > drivers/acpi/Kconfig | 3 + > drivers/acpi/Makefile | 1 + > drivers/acpi/spcr.c | 125 ++++++++++++++++++++++++++++++++++++++++++ > drivers/tty/serial/earlycon.c | 11 +++- > include/linux/acpi.h | 8 +++ > 5 files changed, 146 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 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..31e667e > --- /dev/null > +++ b/drivers/acpi/spcr.c > @@ -0,0 +1,125 @@ > +/* > + * 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> > +#include <linux/of_fdt.h> > + > +static bool earlycon_init_is_deferred __initdata; > + > +void __init defer_earlycon_init(void) > +{ > + earlycon_init_is_deferred = true; > +} > + > +/** > + * parse_spcr() - parse ACPI SPCR table and add preferred console > + * > + * For the architectures with support for ACPI, CONFIG_ACPI_SPCR_TABLE may be > + * defined to parse ACPI SPCR table. As a result of the parsing preferred > + * console is registered. > + * > + * When CONFIG_ACPI_SPCR_TABLE is defined, this function should should be called > + * from arch inintialization code as soon as the DT/ACPI decision is made. > + * > + * When CONFIG_ACPI_SPCR_TABLE is defined, "earlycon" without parameters in > + * command line does not start DT earlycon immediately, instead it defers > + * starting it until DT/ACPI decision is made. If ACPI is enabled at that time, > + * parse_spcr() parses the table, adds preferred console and sets up it as an > + * earlycon. If ACPI is disabled at that time, it tries to set up earlycon > + * from DT. > + */ > +int __init parse_spcr(void) > +{ > +#define OPTS_LEN 64 I'm not sure if you need that symbol. ISTR that sizeof(opts) will give you the size of the array (but maybe I'm confusing this with something else). > + static char opts[OPTS_LEN]; > + struct acpi_table_spcr *table; > + acpi_size table_size; > + acpi_status status; > + char *uart; > + char *iotype; > + int baud_rate; > + int err; > + > + if (acpi_disabled) > + return earlycon_init_is_deferred ? > + early_init_dt_scan_chosen_stdout() : 0; I would prefer this to be arranged differently, so a specific error value is returned when ACPI is disabled and the the fallback to DT happens in the caller (if it cares about DT, that is). > + > + 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; Why -EINVAL? > + pr_err("wrong table version\n"); > + goto done; > + } > + > + iotype = (table->serial_port.space_id == ACPI_ADR_SPACE_SYSTEM_MEMORY) ? The parens are not necessary. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
