[PATCH 3/3] ACPI: SPCR: Add support for rev 3

[Raul E Rangel]

Revision 3 supports specifying the UART input clock. This allows for
proper computation of the UART divisor when the baud rate is specified.

The earlycon code can accept the following format (See `parse_options`
in `earlycon.c`.):
* <name>,io|mmio|mmio32|mmio32be,<addr>,<baud>,<uartclk>,<options>

This change makes it so the uartclk is passed along if it's defined in
the SPCR table.

Booting with `earlycon` and a SPCR v3 table that has the uartclk and
baud defined:
[    0.028251] ACPI: SPCR: console: uart,mmio32,0xfedc9000,115200,48000000
[    0.028267] earlycon: uart0 at MMIO32 0x00000000fedc9000 (options '115200,48000000')
[    0.028272] printk: legacy bootconsole [uart0] enabled

Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table

Signed-off-by: Raul E Rangel <rrangel@xxxxxxxxxxxx>

---

 drivers/acpi/spcr.c   | 5 ++++-
 include/acpi/actbl3.h | 6 +++---
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index cd36a97b0ea2c7..67ae42afcc59ef 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -209,9 +209,12 @@ 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 {
+	} else if (table->header.revision <= 2 || !table->uartclk) {
 		snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
 			 table->serial_port.address, baud_rate);
+	} else {
+		snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d,%d", uart, iotype,
+			 table->serial_port.address, baud_rate, table->uartclk);
 	}
 
 	pr_info("console: %s\n", opts);
diff --git a/include/acpi/actbl3.h b/include/acpi/actbl3.h
index 8f775e3a08fdfb..afe45a2379866a 100644
--- a/include/acpi/actbl3.h
+++ b/include/acpi/actbl3.h
@@ -92,10 +92,10 @@ struct acpi_table_slit {
 /*******************************************************************************
  *
  * SPCR - Serial Port Console Redirection table
- *        Version 2
+ *        Version 3
  *
  * Conforms to "Serial Port Console Redirection Table",
- * Version 1.03, August 10, 2015
+ * Version 1.08, October 7, 2021
  *
  ******************************************************************************/
 
@@ -120,7 +120,7 @@ struct acpi_table_spcr {
 	u8 pci_function;
 	u32 pci_flags;
 	u8 pci_segment;
-	u32 reserved2;
+	u32 uartclk;
 };
 
 /* Masks for pci_flags field above */
-- 
2.46.0.662.g92d0881bb0-goog