Streams: Define a lower level abstraction for queue access

This adds a new pair of interfaces called producer and consumer
which are simpler (in that they don't hold onto the underlying
queue) than the stream interfaces.  This makes it easier to
share a single queue between the endpoints that will manipulate
it.  It was not possible to share a queue between two objects
that implemented the in_stream and out_stream interfaces.

This also adds a pair of adaptors that can convert a producer
or consumer into a stream of the correct type.  These adaptors
will be used for existing code once the usb-stream and usart
drivers are converted over to use the producer/consumer
interfaces instead of the stream interfaces.

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

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

Change-Id: I42b4b1ac15cca28e1adc6d3cea315f15e17a0b4d
Reviewed-on: https://chromium-review.googlesource.com/250941
Trybot-Ready: Anton Staaf <robotboy@chromium.org>
Tested-by: Anton Staaf <robotboy@chromium.org>
Reviewed-by: Randall Spangler <rspangler@chromium.org>
Commit-Queue: Anton Staaf <robotboy@chromium.org>

1 files changed, 81 insertions, 0 deletions

diff --git a/include/consumer.h b/include/consumer.h
new file mode 100644
index 0000000000..4a456de512
--- /dev/null
+++ b/include/consumer.h
@@ -0,0 +1,81 @@
+/* Copyright (c) 2015 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.
+ *
+ * Consumer interface
+ *
+ * The consumer abstraction allows for code that wants to be able to read from
+ * a queue, and be notified of new additions to the queue, or of requests to
+ * flush (empty) the queue.
+ */
+#ifndef INCLUDE_CONSUMER_H
+#define INCLUDE_CONSUMER_H
+
+#include "queue.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+struct consumer;
+struct producer;
+
+struct consumer_ops {
+	/*
+	 * Inform the consumer that count units were written to the queue.
+	 * This gives it the oportunity to read additional units from the queue
+	 * or to wake up a task or interrupt to do the same.  If a consumer has
+	 * no need for this information it can set this to NULL.
+	 */
+	void (*written)(struct consumer const *consumer, size_t count);
+
+	/*
+	 * Flush (read) everything from the associated queue.  This call blocks
+	 * until the consumer has flushed the queue.
+	 */
+	void (*flush)(struct consumer const *consumer);
+};
+
+struct consumer {
+	/*
+	 * A consumer references the producer at the other end of the queue.
+	 * This allows the consumer to notify the producer when units are
+	 * removed from the queue.
+	 */
+	struct producer const *producer;
+
+	/*
+	 * A consumer also references the queue that it is reading from.  This
+	 * and the producer reference above could be more flexibly replaced by
+	 * a queue manager object that could handle multiple producer/consumers
+	 * or alternate notification mechanisms.  But that complexity is not
+	 * yet warranted.
+	 */
+	struct queue const *queue;
+
+	struct consumer_ops const *ops;
+};
+
+/*
+ * Notify the consumer by calling its written method directly, as opposed to
+ * from a deferred callback or another task.
+ */
+void consumer_notify_directly(struct consumer const *consumer, size_t count);
+
+/*
+ * Read a single unit from the queue and notify the associated producer.
+ * Return the number of units read.
+ */
+size_t consumer_read_unit(struct consumer const *consumer, void *unit);
+
+/*
+ * Read multiple units from the queue, using the provided memcpy like routine
+ * and notify the producer.  Return the number of units read.
+ */
+size_t consumer_read_memcpy(struct consumer const *consumer,
+			    void *units,
+			    size_t count,
+			    void *(*memcpy)(void *dest,
+					    void const *src,
+					    size_t n));
+
+#endif /* INCLUDE_CONSUMER_H */