From: Andy Shevchenko andriy.shevchenko@linux.intel.com
[ 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-po...
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/acpi/spcr.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c index 324b35bfe781..f567fa5f0148 100644 --- a/drivers/acpi/spcr.c +++ b/drivers/acpi/spcr.c @@ -148,6 +148,13 @@ int __init parse_spcr(bool earlycon) }
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 parse_spcr(bool earlycon) * 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 {