ACPI: parse SPCR and enable matching console

'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.

Parse the ACPI SPCR table, setup earlycon if required,
enable 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 <aleksey.makarov@linaro.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

6 files changed, 146 insertions, 3 deletions

diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
index 445ce28475b3..a984cc7dcba4 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 5ae9d85c5159..c469516062c6 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile
@@ -81,6 +81,7 @@ 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 000000000000..e8d7bc7d4da8
--- /dev/null
+++ b/drivers/acpi/spcr.c
@@ -0,0 +1,111 @@
+/*
+ * 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>
+
+/**
+ * parse_spcr() - parse ACPI SPCR table and add preferred console
+ *
+ * @earlycon: set up earlycon for the console specified by the table
+ *
+ * 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 and if @earlycon is true, earlycon is set up.
+ *
+ * When CONFIG_ACPI_SPCR_TABLE is defined, this function should be called
+ * from arch inintialization code as soon as the DT/ACPI decision is made.
+ *
+ */
+int __init parse_spcr(bool earlycon)
+{
+        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;
+
+        if (acpi_disabled)
+                return -ENODEV;
+
+        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 = -ENOENT;
+                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;
+        }
+
+        snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
+                 table->serial_port.address, baud_rate);
+
+        pr_info("console: %s\n", opts);
+
+        if (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 836cad222fcc..c3651540e1ba 100644
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c
@@ -21,6 +21,7 @@
 #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>
@@ -198,6 +199,14 @@ int __init setup_earlycon(char *buf)
         return -ENOENT;
 }
 
+/*
+ * 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.  At that time if ACPI is enabled
+ * call parse_spcr(), else call early_init_dt_scan_chosen_stdout()
+ */
+bool earlycon_init_is_deferred __initdata;
+
 /* early_param wrapper for setup_earlycon() */
 static int __init param_setup_earlycon(char *buf)
 {
@@ -207,8 +216,14 @@ static int __init param_setup_earlycon(char *buf)
          * Just 'earlycon' is a valid param for devicetree earlycons;
          * don't generate a warning from parse_early_params() in that case
          */
-        if (!buf || !buf[0])
-                return early_init_dt_scan_chosen_stdout();
+        if (!buf || !buf[0]) {
+                if (IS_ENABLED(CONFIG_ACPI_SPCR_TABLE)) {
+                        earlycon_init_is_deferred = true;
+                        return 0;
+                } else {
+                        return early_init_dt_scan_chosen_stdout();
+                }
+        }
 
         err = setup_earlycon(buf);
         if (err == -ENOENT || err == -EALREADY)
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index c5eaf2f80a4c..2353827731d2 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1074,4 +1074,10 @@ void acpi_table_upgrade(void);
 static inline void acpi_table_upgrade(void) { }
 #endif
 
+#ifdef CONFIG_ACPI_SPCR_TABLE
+int parse_spcr(bool earlycon);
+#else
+static inline int parse_spcr(bool earlycon) { return 0; }
+#endif
+
 #endif  /*_LINUX_ACPI_H*/
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 378d80a8dd43..344201437017 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -367,11 +367,18 @@ extern const struct earlycon_id __earlycon_table_end[];
 
 #define EARLYCON_DECLARE(_name, fn)     OF_EARLYCON_DECLARE(_name, "", fn)
 
-extern int setup_earlycon(char *buf);
 extern int of_setup_earlycon(const struct earlycon_id *match,
                              unsigned long node,
                              const char *options);
 
+#ifdef CONFIG_SERIAL_EARLYCON
+extern bool earlycon_init_is_deferred __initdata;
+int setup_earlycon(char *buf);
+#else
+static const bool earlycon_init_is_deferred;
+static inline int setup_earlycon(char *buf) { return 0; }
+#endif
+
 struct uart_port *uart_get_console(struct uart_port *ports, int nr,
                                    struct console *c);
 int uart_parse_earlycon(char *p, unsigned char *iotype, resource_size_t *addr,