queue-4.14/acpi-spcr-consider-baud-rate-0-as-preconfigured-stat.patch

   1 From 56cc31513311b73874e05d23e2429bf31e1441c2 Mon Sep 17 00:00:00 2001
   2 From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
   3 Date: Wed, 21 Nov 2018 15:43:37 +0200
   4 Subject: ACPI: SPCR: Consider baud rate 0 as preconfigured state
   5
   6 [ Upstream commit b413b1abeb21b4a152c0bf8d1379efa30759b6e3 ]
   7
   8 Since SPCR 1.04 [1] the baud rate of 0 means a preconfigured state of UART.
   9 Assume firmware or bootloader configures console correctly.
  10
  11 [1]: https://docs.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table
  12
  13 Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
  14 Reviewed-by: Prarit Bhargava <prarit@redhat.com>
  15 Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
  16 Signed-off-by: Sasha Levin <sashal@kernel.org>
  17 ---
  18  drivers/acpi/spcr.c | 11 +++++++++++
  19  1 file changed, 11 insertions(+)
  20
  21 diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
  22 index 324b35bfe781..f567fa5f0148 100644
  23 --- a/drivers/acpi/spcr.c
  24 +++ b/drivers/acpi/spcr.c
  25 @@ -148,6 +148,13 @@ int __init parse_spcr(bool earlycon)
  26         }
  27
  28         switch (table->baud_rate) {
  29 +       case 0:
  30 +               /*
  31 +                * SPCR 1.04 defines 0 as a preconfigured state of UART.
  32 +                * Assume firmware or bootloader configures console correctly.
  33 +                */
  34 +               baud_rate = 0;
  35 +               break;
  36         case 3:
  37                 baud_rate = 9600;
  38                 break;
  39 @@ -196,6 +203,10 @@ int __init parse_spcr(bool earlycon)
  40                  * UART so don't attempt to change to the baud rate state
  41                  * in the table because driver cannot calculate the dividers
  42                  */
  43 +               baud_rate = 0;
  44 +       }
  45 +
  46 +       if (!baud_rate) {
  47                 snprintf(opts, sizeof(opts), "%s,%s,0x%llx", uart, iotype,
  48                          table->serial_port.address);
  49         } else {
  50 --
  51 2.19.1
  52