x86: acpi: Let OS know that console already had been initialized

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@linux.intel.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

diff --git a/arch/x86/lib/acpi_table.c b/arch/x86/lib/acpi_table.c
index 66e32f21bdbd84643bcabbe8dc77d515ed91a917..074987e29433929b49c8339ca2fd235a3c6cf91c 100644 (file)
--- 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);
 }