console: 16550: Prepare for skipping initialisation
On some platforms the UART might have already been initialised, for
instance by firmware running before TF-A or by a separate management
processor. In this case it would not be need to initialise it again
(doing so could create spurious characters). But more importantly this
saves us from knowing the right baudrate and the right base clock rate
for the UART. This can lead to more robust and versatile firmware builds.
Allow to skip the 16550 UART initialisation and baud rate divisor
programming, by interpreting an input clock rate of "0" to signify this
case. This will just skip the call to console_16550_core_init, but still
will register the console properly.
Users should just pass 0 as the second parameter, the baudrate (third
parameter) will then be ignored as well.
Fix copy & paste typos in comments for the console_16550_register()
function on the way.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: I9f8fca5b358f878fac0f31dc411358fd160786ee
diff --git a/include/drivers/ti/uart/uart_16550.h b/include/drivers/ti/uart/uart_16550.h
index 32e38f0..2b95fa3 100644
--- a/include/drivers/ti/uart/uart_16550.h
+++ b/include/drivers/ti/uart/uart_16550.h
@@ -87,6 +87,11 @@
* framework. The |console| pointer must point to storage that will be valid
* for the lifetime of the console, such as a global or static local variable.
* Its contents will be reinitialized from scratch.
+ * When |clock| has a value of 0, the UART will *not* be initialised. This
+ * means the UART should already be enabled and the baudrate and clock setup
+ * should have been done already, either by platform specific code or by
+ * previous firmware stages. The |baud| parameter will be ignored in this
+ * case as well.
*/
int console_16550_register(uintptr_t baseaddr, uint32_t clock, uint32_t baud,
console_16550_t *console);