From: Chen Pei <cp0613@xxxxxxxxxxxxxxxxx> The Microsoft Serial Port Console Redirection (SPCR) specification revision 1.09 comprises additional field: Precise Baud Rate [1]. It is used to describe non-traditional baud rates (such as those used by high-speed UARTs). It contains a specific non-zero baud rate which overrides the value of the Configured Baud Rate field. If this field is zero or not present, Configured Baud Rate is used. Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table # 1 Signed-off-by: Chen Pei <cp0613@xxxxxxxxxxxxxxxxx> --- drivers/acpi/spcr.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c index cd36a97b0ea2..fa12e740386d 100644 --- a/drivers/acpi/spcr.c +++ b/drivers/acpi/spcr.c @@ -146,7 +146,15 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console) goto done; } - switch (table->baud_rate) { + /* + * SPCR 1.09 defines Precise Baud Rate Filed contains a specific + * non-zero baud rate which overrides the value of the Configured + * Baud Rate field. If this field is zero or not present, Configured + * Baud Rate is used. + */ + if (table->precise_baudrate) + baud_rate = table->precise_baudrate; + else switch (table->baud_rate) { case 0: /* * SPCR 1.04 defines 0 as a preconfigured state of UART. -- 2.49.0
