common: uart: split off printf and like functions into separate module

This separates the high-level uart output functions like uart_printf
and uart_putc from the uart buffering module, allowing the buffering
to be implemented separately from the output functions.

The contract between this module and the uart_buffering layer is to
implement uart_tx_char_raw and uart_tx_start.

BUG=b:178033156
BRANCH=none
TEST=buildall

Signed-off-by: Jack Rosenthal <jrosenth@chromium.org>
Change-Id: I5fb62ca2be1fea04654eaadd7a3806ac0c586929
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2685411
Reviewed-by: Simon Glass <sjg@chromium.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/include/uart.h b/include/uart.h
index b6dce4f21f..95df22d5bd 100644
--- a/include/uart.h
+++ b/include/uart.h
@@ -85,6 +85,22 @@ int uart_printf(const char *format, ...);
 int uart_vprintf(const char *format, va_list args);
 
 /**
+ * Put a single character into the transmit buffer.
+ *
+ * Does not enable the transmit interrupt; assumes that happens elsewhere.
+ *
+ * @param context	Context; ignored.
+ * @param c		Character to write.
+ * @return 0 if the character was transmitted, 1 if it was dropped.
+ *
+ * Note: This is intended to be implemented by the UART buffering
+ * module, and called only by the implementations of the uart_*
+ * functions.  You should stick to the higher level functions, such as
+ * uart_putc, outside of the UART implementation.
+ */
+int uart_tx_char_raw(void *context, int c);
+
+/**
  * Flush output.  Blocks until UART has transmitted all output.
  */
 void uart_flush_output(void);