cr50: use RXILVL to trigger fewer UART RXINTs

This change sets UART_FIFO_RXILVL to 3 for the AP and EC UART. With this
change RXINT will only be triggered when 4 characters are received
instead of for every character.

The change also flushes the RX FIFO whenever console input is received
through usb make sure to the user can see their input as they are typing.

BUG=none
BRANCH=none
TEST=run taskinfo after the system finishes booting.

	Before Change the IRQ count for 181 should be around 20000.
	After the change it should be around 5000.

	Use the AP and EC console over USB and verify there is no
        noticeable change in their usability.

Change-Id: I134ea0d2bc254038dad6c341b94f822adb90c000
Signed-off-by: Mary Ruthven <mruthven@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/387175
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

chip/g/uartn.c

@@ -147,6 +147,15 @@ void uartn_init(int uart)
 	 */
 	GR_UART_FIFO(uart) = 0x63;
 
+	/*
+	 * To reduce the number of UART RX interrupts on the peripheral UARTS,
+	 * set the FIFO RXILVL to only trigger rx interrupts every 4 characters.
+	 *
+	 * Reset the RX FIFO.
+	 */
+	if (uart)
+		GR_UART_FIFO(uart) |= 0x7;
+
 	/* enable RX interrupts in block */
 	/* Note: doesn't do anything unless turned on in NVIC */
 	GR_UART_ICTRL(uart) = 0x02;

chip/g/usart.c

@@ -5,6 +5,7 @@
 
 #include "queue.h"
 #include "queue_policies.h"
+#include "timer.h"
 #include "uartn.h"
 #include "usart.h"
 #include "usb-stream.h"
@@ -29,12 +30,15 @@ static struct queue const ec_uart_to_usb =
 static struct queue const ec_usb_to_uart =
 	QUEUE_DIRECT(QUEUE_SIZE, uint8_t, ec_usb.producer, ec_uart.consumer);
 
-struct usart_config const ap_uart = USART_CONFIG(UART_AP,
-						 ap_uart_to_usb,
-						 ap_usb_to_uart);
-struct usart_config const ec_uart = USART_CONFIG(UART_EC,
-						 ec_uart_to_usb,
-						 ec_usb_to_uart);
+USART_CONFIG(ec_uart,
+	     UART_EC,
+	     ec_uart_to_usb,
+	     ec_usb_to_uart);
+USART_CONFIG(ap_uart,
+	     UART_AP,
+	     ap_uart_to_usb,
+	     ap_usb_to_uart);
+
 USB_STREAM_CONFIG(ap_usb,
 		  USB_IFACE_AP,
 		  USB_STR_AP_NAME,
@@ -64,6 +68,13 @@ void get_data_from_usb(struct usart_config const *config)
 	/* If output buffer is empty, disable transmit interrupt */
 	if (!queue_count(uart_out))
 		uartn_tx_stop(config->uart);
+
+	/*
+	 * Make sure rx fifo is cleared after any input to the console to ensure
+	 * user will be able to see their input as they are typing instead of
+	 * only when the RX FIFO reaches the level set by RXILVL.
+	 */
+	hook_call_deferred(config->deferred, 1 * MSEC);
 }
 
 void send_data_to_usb(struct usart_config const *config)

chip/g/usart.h

@@ -16,6 +16,8 @@ struct usart_config {
 
 	struct producer const producer;
 	struct consumer const consumer;
+
+	const struct deferred_data *deferred;
 };
 
 extern struct consumer_ops const uart_consumer_ops;
@@ -41,14 +43,17 @@ extern struct producer_ops const uart_producer_ops;
 		GR_UART_ISTATECLR(NAME.uart) =				\
 			GC_UART_ISTATECLR_RX_MASK;			\
 		/* Read input FIFO until empty */			\
-		send_data_to_usb(&NAME);				\
+		hook_call_deferred(NAME.deferred, 0);			\
 	}
 
 
-#define USART_CONFIG(UART,						\
+#define USART_CONFIG(NAME,						\
+		     UART,						\
 		     RX_QUEUE,						\
 		     TX_QUEUE)						\
-	((struct usart_config const) {					\
+	static void CONCAT2(NAME, _deferred_)(void);			\
+	DECLARE_DEFERRED(CONCAT2(NAME, _deferred_));			\
+	struct usart_config const NAME = {				\
 		.uart      = UART,					\
 		.consumer  = {						\
 			.queue = &TX_QUEUE,				\
@@ -58,7 +63,12 @@ extern struct producer_ops const uart_producer_ops;
 			.queue = &RX_QUEUE,				\
 			.ops   = &uart_producer_ops,			\
 		},							\
-	})
+		.deferred  = &CONCAT2(NAME, _deferred__data),		\
+	};								\
+	static void CONCAT2(NAME, _deferred_)(void)			\
+	{								\
+		send_data_to_usb(&NAME);				\
+	}								\
 
 
 /* Read data from UART and add it to the producer queue */