fix(cadence): update console flush uart driver

The implementation of code changes manages the transmit FIFO (TxFIFO)
in the UART driver. The added code snippet includes a sequence of
instructions that ensures efficient handling of data transmission
and synchronization with the host software.

The code first checks the TxFIFO empty flag to determine whether
there is data available for transmission. If the TxFIFO is not empty,
the code waits until it becomes empty, ensuring that the transmit
operation is synchronized with the availability of data.
Subsequently, the code monitors the transmit operation's activity
status. It waits until the transmit operation becomes inactive,
indicating the completion of the previous transmission.

This synchronization step ensures that new data can be added to the
TxFIFO without causing any loss of transmission time.

Update console_flush() function, the function waits for the
Transmitter FIFO to empty and checks the transmitter's active state.
If the transmitter is in an active state, it means it is currently
shifting out a character.

Signed-off-by: Prasad Kummari <prasad.kummari@amd.com>
Change-Id: I9d6c05bdfb9270924b40bf1f6ecb5fe541a2242e

drivers/cadence/uart/aarch64/cdns_console.S

@@ -197,7 +197,14 @@ func console_cdns_core_flush
 	cmp	x0, #0
 	ASM_ASSERT(ne)
 #endif /* ENABLE_ASSERTIONS */
-	/* Placeholder */
+	/* Loop until the transmit FIFO is empty */
+check_txfifo_empty:
+	ldr     w2, [x0, #R_UART_SR]
+	tbz     w2, #UART_SR_INTR_TEMPTY_BIT, check_txfifo_empty
+	/* Wait until the Transmit is Inactive */
+check_tx_inactive_state:
+	ldr     w2, [x0, #R_UART_SR]
+	tbnz    w2, #UART_SR_INTR_TACTIVE_BIT, check_tx_inactive_state
 	ret
 endfunc console_cdns_core_flush
 

include/drivers/cadence/cdns_uart.h

@@ -22,6 +22,7 @@
 #define UART_SR_INTR_REMPTY_BIT	1
 #define UART_SR_INTR_TFUL_BIT	4
 #define UART_SR_INTR_TEMPTY_BIT	3
+#define UART_SR_INTR_TACTIVE_BIT	11
 
 #define R_UART_TX	0x30
 #define R_UART_RX	0x30