Add example implementation of a trivial blocking read function as a
part of Barebox's serdev API.

NOTE: This code has not been tested against real devices, so use it at
your own risk.

Signed-off-by: Andrey Smirnov <andrew.smir...@gmail.com>
---
 common/serdev.c  | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/serdev.h |  8 +++++
 2 files changed, 103 insertions(+)

diff --git a/common/serdev.c b/common/serdev.c
index 32743738e..50eadc804 100644
--- a/common/serdev.c
+++ b/common/serdev.c
@@ -87,3 +87,98 @@ int serdev_device_write(struct serdev_device *serdev, const 
unsigned char *buf,
        serdev_device_poller(serdev);
        return 0;
 }
+
+/*
+ * NOTE: Code below is given primarily as an example of serdev API
+ * usage. It may or may not be as useful or work as well as the
+ * functions above.
+ */
+
+struct serdev_device_reader {
+       unsigned char *buf;
+       size_t len;
+       size_t capacity;
+};
+
+static int serdev_device_reader_receive_buf(struct serdev_device *serdev,
+                                           const unsigned char *buf,
+                                           size_t size)
+{
+       struct device_d *dev = serdev->dev;
+       struct serdev_device_reader *r = dev->priv;
+       const size_t room = min(r->capacity - r->len, size);
+
+       memcpy(r->buf + r->len, buf, room);
+       r->len += room;
+       /*
+        * It's important we return 'size' even if we didn't trully
+        * consume all of the data, since otherwise serdev will keep
+        * re-executing us until we do. Given the logic above that
+        * would mean infinite loop.
+        */
+       return size;
+}
+
+/**
+ * serdev_device_reader_open - Open a reader serdev device
+ *
+ * @serdev:    Underlying serdev device
+ * @capacity:  Storage capacity of the reader
+ *
+ * This function is inteded for creating of reader serdev devices that
+ * can be used in conjunction with serdev_device_read() to perform
+ * trivial fixed length reads from a serdev device.
+ */
+int serdev_device_reader_open(struct serdev_device *serdev, size_t capacity)
+{
+       struct serdev_device_reader *r;
+
+       if (serdev->receive_buf)
+               return -EINVAL;
+
+       r = xzalloc(sizeof(*r));
+       r->capacity = capacity;
+       r->buf = xzalloc(capacity);
+
+       serdev->receive_buf = serdev_device_reader_receive_buf;
+       serdev->dev->priv   = r;
+
+       return 0;
+}
+
+/**
+ * serdev_device_read - Read data from serdev device
+ *
+ * @serdev:    Serdev device to read from (must be a serdev reader)
+ * @buf:       Buffer to read data into
+ * @count:     Number of bytes to read
+ * @timeout:   Read operation timeout
+ *
+ */
+int serdev_device_read(struct serdev_device *serdev, unsigned char *buf,
+                      size_t count, unsigned long timeout)
+{
+       struct device_d *dev = serdev->dev;
+       struct serdev_device_reader *r = dev->priv;
+       int ret;
+
+       uint64_t start = get_time_ns();
+
+       if (serdev->receive_buf != serdev_device_reader_receive_buf)
+               return -EINVAL;
+
+       /*
+        * is_timeout will implicitly poll serdev via poller
+        * infrastructure
+        */
+       while (r->len < count) {
+               if (is_timeout(start, timeout))
+                       return -ETIMEDOUT;
+       }
+
+       memcpy(buf, r->buf, count);
+       ret = (r->len == count) ? 0 : -EMSGSIZE;
+       r->len = 0;
+
+       return ret;
+}
diff --git a/include/serdev.h b/include/serdev.h
index efc735fed..f5d34f527 100644
--- a/include/serdev.h
+++ b/include/serdev.h
@@ -33,4 +33,12 @@ int serdev_device_open(struct serdev_device *);
 unsigned int serdev_device_set_baudrate(struct serdev_device *, unsigned int);
 int serdev_device_write(struct serdev_device *, const unsigned char *,
                        size_t, unsigned long);
+
+/*
+ * The following two functions are not a part of original Linux API
+ */
+int serdev_device_reader_open(struct serdev_device *, size_t);
+int serdev_device_read(struct serdev_device *, unsigned char *,
+                      size_t, unsigned long);
+
 #endif
-- 
2.14.3


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