From 4d330fe54145ecfbb657ac01a554fdedf3c1927e Mon Sep 17 00:00:00 2001 From: Chen Pei Date: Sat, 13 Sep 2025 15:08:15 +0800 Subject: [PATCH] ACPI: SPCR: Support Precise Baud Rate field 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 Link: https://patch.msgid.link/20250913070815.16758-1-cp0613@linux.alibaba.com [ rjw: Corrected typo in the subject ] Signed-off-by: Rafael J. Wysocki --- 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 208d6bbc65e0..d4d52d5e9016 100644 --- a/drivers/acpi/spcr.c +++ b/drivers/acpi/spcr.c @@ -149,7 +149,15 @@ 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. -- 2.20.1