From 53a0714c81b1584f1fe41e13b1a05dca632f6509 Mon Sep 17 00:00:00 2001 From: Julien Grall Date: Sun, 28 Apr 2013 20:14:12 +0100 Subject: xen/arm: Don't use pl011 UART by default for early printk Add CONFIG_EARLY_PRINTK options in configs/arm{32,64}.mk to let the user to choose if he wants to have early output, ie before the console is initialized. This code is specific for each UART. When CONFIG_EARLY_PRINTK is enabled, Xen will only be able to run on a board with this UART. If a developper wants to add support for a new UART, he must implement the following assembly macro/define: - EALY_UART_BASE_ADDRESS: variable which contains the physical base address for the UART - early_uart_init: initialize the UART - early_uart_ready: check and wait until the UART can transmit a new character - early_uart_transmit: transmit a character For more details about the parameters of each function, see arm{32,64}/debug-pl011.inc comments. Signed-off-by: Julien Grall Acked-by: Ian Campbell --- docs/misc/arm/early-printk.txt | 14 ++++++++++++++ 1 file changed, 14 insertions(+) create mode 100644 docs/misc/arm/early-printk.txt (limited to 'docs') diff --git a/docs/misc/arm/early-printk.txt b/docs/misc/arm/early-printk.txt new file mode 100644 index 0000000000..4065811e82 --- /dev/null +++ b/docs/misc/arm/early-printk.txt @@ -0,0 +1,14 @@ +How to enable early printk + +Early printk can only be enabled if debug=y. You may want to enable it if +you are debbuging code that executes before the console is initialized. + +Note that selecting this option will limit Xen to a single UART definition. +Attempting to boot Xen image on a different platform *will not work*, so this +option should not be enable for Xens that are intended to be portable. + +CONFIG_EARLY_PRINTK=mach +where mach is the name of the machine: + - vexpress: printk with pl011 for versatile express + +By default early printk is disabled. -- cgit v1.2.3