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nios2: enable earlycon support

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Enable generic earlycon support for nios2. This e.g. allows to use a
8250/16650 UART as earlycon.

In order to get the earlycon, we just need to call parse_early_param()
in early_init_devtree() as soon as the device tree is initially scanned.
By adding an stdout-path property to the dts (done in this patch for
10m50_devboard), the earlycon can be used.

In order to provide early printk support, we need to provide a dummy
implementation of early_console_write(), so that
arch/nios2/kernel/early_printk.c can still be compiled if neither
SERIAL_ALTERA_JTAGUART_CONSOLE nor SERIAL_ALTERA_UART_CONSOLE is
selected. As soon as the altera_uart and altera_jtaguart support
earlycon, the entire file can be removed.

Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Acked-by: Ley Foon Tan <ley.foon.tan@intel.com>
This commit is contained in:
Tobias Klauser
2017-04-02 20:09:04 -07:00
committed by Ley Foon Tan
parent 57ac76ed6c
commit 44a4ed4257
4 changed files with 9 additions and 4 deletions
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arch/nios2/Kconfig.debug
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@@ -18,7 +18,6 @@ config EARLY_PRINTK
bool "Activate early kernel debugging"
default y
select SERIAL_CORE_CONSOLE
depends on SERIAL_ALTERA_JTAGUART_CONSOLE || SERIAL_ALTERA_UART_CONSOLE
help
Enable early printk on console
This is useful for kernel debugging when your machine crashes very