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ACPI: SPCR: Consider baud rate 0 as preconfigured state 

Since SPCR 1.04 [1] the baud rate of 0 means a preconfigured state of UART.
Assume firmware or bootloader configures console correctly.

[1]: https://docs.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Andy Shevchenko 2018-11-21 15:43:37 +02:00 committed by Rafael J. Wysocki
parent 2e6e902d18
commit b413b1abeb
1 changed files with 11 additions and 0 deletions
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11
drivers/acpi/spcr.c
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@ -148,6 +148,13 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
}
switch (table->baud_rate) {
case 0:
/*
* SPCR 1.04 defines 0 as a preconfigured state of UART.
* Assume firmware or bootloader configures console correctly.
*/
baud_rate = 0;
break;
case 3:
baud_rate = 9600;
break;
@ -196,6 +203,10 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
* UART so don't attempt to change to the baud rate state
* in the table because driver cannot calculate the dividers
*/
baud_rate = 0;
}
if (!baud_rate) {
snprintf(opts, sizeof(opts), "%s,%s,0x%llx", uart, iotype,
table->serial_port.address);
} else {