[PATCH] ACPI: SPCR: Support UART clock frequency field

[Markus Probst]

The Microsoft Serial Port Console Redirection (SPCR) specification
revision 1.08 comprises additional field: UART Clock Frequency [1].

It contains a non-zero value indicating the UART clock frequency in Hz.

Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table [1]
Signed-off-by: Markus Probst <markus.probst@xxxxxxxxx>
---
 drivers/acpi/spcr.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index 73cb933fdc89..d80ad87efae0 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -220,6 +220,9 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
 	if (!baud_rate) {
 		snprintf(opts, sizeof(opts), "%s,%s,0x%llx", uart, iotype,
 			 table->serial_port.address);
+	} else if (table->header.revision >= 3 && table->uart_clk_freq) {
+		snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d,%u", uart, iotype,
+			table->serial_port.address, baud_rate, table->uart_clk_freq);
 	} else {
 		snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
 			 table->serial_port.address, baud_rate);

---
base-commit: 9e0898f1c0f134c6bad146ca8578f73c3e40ac0a
change-id: 20260430-acpi_spcr-61902fd923f2