From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> [ Upstream commit b413b1abeb21b4a152c0bf8d1379efa30759b6e3 ] 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@xxxxxxxxxxxxxxx> Reviewed-by: Prarit Bhargava <prarit@xxxxxxxxxx> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- drivers/acpi/spcr.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c index 9d52743080a4..c336784d0bcb 100644 --- a/drivers/acpi/spcr.c +++ b/drivers/acpi/spcr.c @@ -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 { -- 2.19.1
