USART: Add flexibility needed to support DMA

In order to support DMA transfers in one or both directions the usart
driver needs to be configurable with producer/consumer operations and
interrupt handler functions.  These are now packaged up in the usart_rx
and usart_tx structs, and versions for interrupt driven RX and TX are
provided.

Signed-off-by: Anton Staaf <robotboy@chromium.org>

BRANCH=None
BUG=None
TEST=make buildall -j

Change-Id: I3fd14c675c90873e903195b8e20d2070d2eda5ac
Reviewed-on: https://chromium-review.googlesource.com/285023
Trybot-Ready: Anton Staaf <robotboy@chromium.org>
Tested-by: Anton Staaf <robotboy@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>
Tested-by: Todd Broch <tbroch@chromium.org>
Commit-Queue: Anton Staaf <robotboy@chromium.org>

1 files changed, 48 insertions, 0 deletions

diff --git a/chip/stm32/usart_rx_interrupt.c b/chip/stm32/usart_rx_interrupt.c
new file mode 100644
index 0000000000..6a46b3fb11
--- /dev/null
+++ b/chip/stm32/usart_rx_interrupt.c
@@ -0,0 +1,48 @@
+/* Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Interrupt based USART RX driver for STM32 */
+
+#include "usart.h"
+
+#include "atomic.h"
+#include "common.h"
+#include "queue.h"
+#include "registers.h"
+
+static void usart_rx_init(struct usart_config const *config)
+{
+	intptr_t base = config->hw->base;
+
+	STM32_USART_CR1(base) |= STM32_USART_CR1_RXNEIE;
+	STM32_USART_CR1(base) |= STM32_USART_CR1_RE;
+}
+
+static void usart_rx_interrupt_handler(struct usart_config const *config)
+{
+	intptr_t base = config->hw->base;
+	uint8_t  byte;
+
+	if (!(STM32_USART_SR(base) & STM32_USART_SR_RXNE))
+		return;
+
+	byte = STM32_USART_RDR(base);
+
+	if (!queue_add_unit(config->producer.queue, &byte))
+		atomic_add((uint32_t *) &config->state->rx_dropped, 1);
+}
+
+struct usart_rx const usart_rx_interrupt = {
+	.producer_ops = {
+		/*
+		 * Nothing to do here, we either had enough space in the queue
+		 * when a character came in or we dropped it already.
+		 */
+		.read = NULL,
+	},
+
+	.init      = usart_rx_init,
+	.interrupt = usart_rx_interrupt_handler,
+};