On 03/22/2016 04:09 AM, Andy Shevchenko wrote:

On Tue, Mar 22, 2016 at 12:46 PM, Aleksey Makarov
[off-list ref] wrote:

quoted

'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.

Parse this table, setup earlycon and enable the 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

quoted

+++ b/drivers/acpi/spcr.c

@@ -0,0 +1,102 @@
+/*
+ * 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>
+
+static bool init_earlycon;
+
+void __init init_spcr_earlycon(void)
+{
+       init_earlycon = true;
+}
+
+int __init parse_spcr(void)
+{
+       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 = 0;
+
+       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;
+               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;
+       }
+
+       sprintf(opts, "%s,%s,0x%llx,%d", uart, iotype,
+               table->serial_port.address, baud_rate);

You may use snprintf(), though my question here what would happen on
32-bit kernel when you supply 64-bit address as an option?

Yeah this should probably use %pa for the printf specifier.

But note this exposes underlying bug in the earlycon support, because
that was originally written without 32/64-mixed bitness in mind; ie.,
the address is parsed and handled as unsigned long in most places.

quoted

+
+       pr_info("console: %s", opts);
+
+       if (init_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 d217366..ec030c9 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>

@@ -206,11 +207,15 @@ 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 and ACPI SPCR
+        * earlycons; don't generate a warning from parse_early_params()
+        * in that case
         */
-       if (!buf || !buf[0])
-               return early_init_dt_scan_chosen_serial();
+       if (!buf || !buf[0]) {
+               init_spcr_earlycon();

quoted

+               early_init_dt_scan_chosen_serial();
+               return 0;

And you hide an error?

Well, this is a little bit tricky because "earlycon" early parameter with
missing /chosen/stdout-path node is no longer an error, since ACPI may be
specifying the earlycon instead.

Regards,
Peter Hurley

quoted

+       }

        err = setup_earlycon(buf);
        if (err == -ENOENT || err == -EALREADY)