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Subject[PATCH 4.14 040/205] ACPI: SPCR: Consider baud rate 0 as preconfigured state
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit b413b1abeb21b4a152c0bf8d1379efa30759b6e3 ]

Since SPCR 1.04 [1] the baud rate of 0 means a preconfigured state of UART.
Assume firmware or bootloader configures console correctly.

[1]: https://docs.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/acpi/spcr.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
index 324b35bfe781..f567fa5f0148 100644
--- a/drivers/acpi/spcr.c
+++ b/drivers/acpi/spcr.c
@@ -148,6 +148,13 @@ int __init parse_spcr(bool earlycon)
}

switch (table->baud_rate) {
+ case 0:
+ /*
+ * SPCR 1.04 defines 0 as a preconfigured state of UART.
+ * Assume firmware or bootloader configures console correctly.
+ */
+ baud_rate = 0;
+ break;
case 3:
baud_rate = 9600;
break;
@@ -196,6 +203,10 @@ int __init parse_spcr(bool earlycon)
* UART so don't attempt to change to the baud rate state
* in the table because driver cannot calculate the dividers
*/
+ baud_rate = 0;
+ }
+
+ if (!baud_rate) {
snprintf(opts, sizeof(opts), "%s,%s,0x%llx", uart, iotype,
table->serial_port.address);
} else {
--
2.19.1


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