Re: [PATCH v5 3/6] ACPI: parse SPCR and enable matching console

[Peter Hurley]

On 03/22/2016 04:09 AM, Andy Shevchenko wrote:
> On Tue, Mar 22, 2016 at 12:46 PM, Aleksey Makarov
> <aleksey.makarov@xxxxxxxxxx> 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.
>>
>> 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
>>
> 
>> +++ 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.




>> +
>> +       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();
> 
>> +               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

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