AMD Carrizo / Stoneyridge use a DesignWare 8250 UART that uses a 48 MHz input clock. Currently, there is no way to tell earlycon to use a specific uart input clock when configuring a baud rate.
Patch 1 adds an earlycon ->setup() callback to set up this clock. The setup is triggered on the commandline by specifying "earlycon=amdcz,...". Patch 2 adds an ACPI SPCR quirk to automatically trigger this hook when the ACPI SPCR table OEMID field is "AMDCZ ". Patch 3 adds an additional fix which allows botht the ACPI SPCR quirk and amdcz ->setup() to tell 8250_core to skip initialization of old serial ports that do not exist on these SoCs. Daniel Kurtz (3): serial: 8250_early: Add earlycon support for AMD Carrizo / Stoneyridge ACPI: SPCR: Add support for AMD CT/SZ serial: core: Allow skipping old serial port initialization drivers/acpi/spcr.c | 26 ++++++++++++++++++++++++++ drivers/tty/serial/8250/8250_core.c | 6 ++++++ drivers/tty/serial/8250/8250_early.c | 16 ++++++++++++++++ include/linux/serial_8250.h | 2 ++ 4 files changed, 50 insertions(+) -- 2.16.2.804.g6dcf76e118-goog
