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 | 56 ++++++++++++++++++++++++++------------------- 1 file changed, 33 insertions(+), 23 deletions(-) diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c index cd36a97b0ea2..69142c2ac4b3 100644 --- a/drivers/acpi/spcr.c +++ b/drivers/acpi/spcr.c @@ -146,29 +146,39 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console) goto done; } - 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; - case 4: - baud_rate = 19200; - break; - case 6: - baud_rate = 57600; - break; - case 7: - baud_rate = 115200; - break; - default: - err = -ENOENT; - goto done; + /* + * 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. + * Assume firmware or bootloader configures console correctly. + */ + baud_rate = 0; + break; + case 3: + baud_rate = 9600; + break; + case 4: + baud_rate = 19200; + break; + case 6: + baud_rate = 57600; + break; + case 7: + baud_rate = 115200; + break; + default: + err = -ENOENT; + goto done; + } } /* -- 2.49.0
