On Fri, Sep 12, 2025 at 2:25 PM <cp0613@xxxxxxxxxxxxxxxxx> wrote: > > 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 | 54 ++++++++++++++++++++++++++------------------- > 1 file changed, 31 insertions(+), 23 deletions(-) > > diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c > index cd36a97b0ea2..a97b02ee5538 100644 > --- a/drivers/acpi/spcr.c > +++ b/drivers/acpi/spcr.c > @@ -146,29 +146,37 @@ 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) { Please do not change the indentation below. > + 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 >
