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author | Julien Grall <julien.grall@linaro.org> | 2013-04-28 20:14:12 +0100 |
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committer | Ian Campbell <ian.campbell@citrix.com> | 2013-05-13 12:00:01 +0100 |
commit | 53a0714c81b1584f1fe41e13b1a05dca632f6509 (patch) | |
tree | 79fa9a97fc26df8b7358c12a5aeb3d401c5475c9 /docs | |
parent | 237c94508b149af506e20dd1ad8bcd57b49201f9 (diff) | |
download | xen-53a0714c81b1584f1fe41e13b1a05dca632f6509.tar.gz xen-53a0714c81b1584f1fe41e13b1a05dca632f6509.tar.bz2 xen-53a0714c81b1584f1fe41e13b1a05dca632f6509.zip |
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 <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Diffstat (limited to 'docs')
-rw-r--r-- | docs/misc/arm/early-printk.txt | 14 |
1 files changed, 14 insertions, 0 deletions
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. |