[PATCH v1 3/3] x86: acpi: Let OS know that console already had been initialized

[Andy Shevchenko]

SPCR has no clue if the UART base clock speed is different to
the default one. However, the SPCR 1.04 defines baud rate 0 as
a preconfigured state of UART and OS is supposed not to touch
the configuration of the serial device.

Linux kernel supports that starting from v5.0, see commit
b413b1abeb21 ("ACPI: SPCR: Consider baud rate 0 as preconfigured state")
for the details.

Signed-off-by: Andy Shevchenko <andriy.shevchenko at linux.intel.com>
---
 arch/x86/lib/acpi_table.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/lib/acpi_table.c b/arch/x86/lib/acpi_table.c
index 66e32f21bd..074987e294 100644
--- a/arch/x86/lib/acpi_table.c
+++ b/arch/x86/lib/acpi_table.c
@@ -471,6 +471,15 @@ static void acpi_create_spcr(struct acpi_spcr *spcr)
 	spcr->pci_device_id = 0xffff;
 	spcr->pci_vendor_id = 0xffff;
 
+	/*
+	 * SPCR has no clue if the UART base clock speed is different
+	 * to the default one. However, the SPCR 1.04 defines baud rate
+	 * 0 as a preconfigured state of UART and OS is supposed not
+	 * to touch the configuration of the serial device.
+	 */
+	if (serial_info.clock != SERIAL_DEFAULT_CLOCK)
+		spcr->baud_rate = 0;
+
 	/* Fix checksum */
 	header->checksum = table_compute_checksum((void *)spcr, header->length);
 }
-- 
2.25.0