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Message-Id: <1403270104-26365-1-git-send-email-abbotti@mev.co.uk>
Date: Fri, 20 Jun 2014 14:15:04 +0100
From: Ian Abbott <abbotti@....co.uk>
To: driverdev-devel@...uxdriverproject.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Ian Abbott <abbotti@....co.uk>,
H Hartley Sweeten <hartleys@...ionengravers.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH] staging: comedi: describe struct comedi_async
Describe `struct comedi_async` in kerneldoc format. Expand on the
members involved in reading/writing the buffer.
Signed-off-by: Ian Abbott <abbotti@....co.uk>
---
This replaces a previous patch titled "staging: comedi: describe members
involved when reading/writing buffer", Message-ID:
<1401970286-32676-1-git-send-email-abbotti@....co.uk>
---
drivers/staging/comedi/comedidev.h | 117 +++++++++++++++++++++++++++++--------
1 file changed, 92 insertions(+), 25 deletions(-)
diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
index 8f4e44b..71851bd 100644
--- a/drivers/staging/comedi/comedidev.h
+++ b/drivers/staging/comedi/comedidev.h
@@ -107,43 +107,110 @@ struct comedi_buf_map {
struct kref refcount;
};
+/**
+ * struct comedi_async - control data for asynchronous comedi commands
+ * @prealloc_buf: preallocated buffer
+ * @prealloc_bufsz: buffer size (in bytes)
+ * @buf_map: map of buffer pages
+ * @max_bufsize: maximum buffer size (in bytes)
+ * @buf_write_count: "write completed" count (in bytes, modulo 2**32)
+ * @buf_write_alloc_count: "allocated for writing" count (in bytes,
+ * modulo 2**32)
+ * @buf_read_count: "read completed" count (in bytes, modulo 2**32)
+ * @buf_read_alloc_count: "allocated for reading" count (in bytes,
+ * modulo 2**32)
+ * @buf_write_ptr: buffer position for writer
+ * @buf_read_ptr: buffer position for reader
+ * @cur_chan: current position in chanlist for scan (for those
+ * drivers that use it)
+ * @scan_progress: amount received or sent for current scan (in bytes)
+ * @munge_chan: current position in chanlist for "munging"
+ * @munge_count: "munge" count (in bytes, modulo 2**32)
+ * @munge_ptr: buffer position for "munging"
+ * @events: bit-vector of events that have occurred
+ * @cmd: details of comedi command in progress
+ * @wait_head: task wait queue for file reader or writer
+ * @cb_mask: bit-vector of events that should wake waiting tasks
+ * @inttrig: software trigger function for command, or NULL
+ *
+ * Note about the ..._count and ..._ptr members:
+ *
+ * Think of the _Count values being integers of unlimited size, indexing
+ * into a buffer of infinite length (though only an advancing portion
+ * of the buffer of fixed length prealloc_bufsz is accessible at any time).
+ * Then:
+ *
+ * Buf_Read_Count <= Buf_Read_Alloc_Count <= Munge_Count <=
+ * Buf_Write_Count <= Buf_Write_Alloc_Count <=
+ * (Buf_Read_Count + prealloc_bufsz)
+ *
+ * (Those aren't the actual members, apart from prealloc_bufsz.) When
+ * the buffer is reset, those _Count values start at 0 and only increase
+ * in value, maintaining the above inequalities until the next time the
+ * buffer is reset. The buffer is divided into the following regions by
+ * the inequalities:
+ *
+ * [0, Buf_Read_Count):
+ * old region no longer accessible
+ * [Buf_Read_Count, Buf_Read_Alloc_Count):
+ * filled and munged region allocated for reading but not yet read
+ * [Buf_Read_Alloc_Count, Munge_Count):
+ * filled and munged region not yet allocated for reading
+ * [Munge_Count, Buf_Write_Count):
+ * filled region not yet munged
+ * [Buf_Write_Count, Buf_Write_Alloc_Count):
+ * unfilled region allocated for writing but not yet written
+ * [Buf_Write_Alloc_Count, Buf_Read_Count + prealloc_bufsz):
+ * unfilled region not yet allocated for writing
+ * [Buf_Read_Count + prealloc_bufsz, infinity):
+ * unfilled region not yet accessible
+ *
+ * Data needs to be written into the buffer before it can be read out,
+ * and may need to be converted (or "munged") between the two
+ * operations. Extra unfilled buffer space may need to allocated for
+ * writing (advancing Buf_Write_Alloc_Count) before new data is written.
+ * After writing new data, the newly filled space needs to be released
+ * (advancing Buf_Write_Count). This also results in the new data being
+ * "munged" (advancing Munge_Count). Before data is read out of the
+ * buffer, extra space may need to be allocated for reading (advancing
+ * Buf_Read_Alloc_Count). After the data has been read out, the space
+ * needs to be released (advancing Buf_Read_Count).
+ *
+ * The actual members, buf_read_count, buf_read_alloc_count,
+ * munge_count, buf_write_count, and buf_write_alloc_count take the
+ * value of the corresponding capitalized _Count values modulo 2^32
+ * (UINT_MAX+1). Subtracting a "higher" _count value from a "lower"
+ * _count value gives the same answer as subtracting a "higher" _Count
+ * value from a lower _Count value because prealloc_bufsz < UINT_MAX+1.
+ * The modulo operation is done implicitly.
+ *
+ * The buf_read_ptr, munge_ptr, and buf_write_ptr members take the value
+ * of the corresponding capitalized _Count values modulo prealloc_bufsz.
+ * These correspond to byte indices in the physical buffer. The modulo
+ * operation is done by subtracting prealloc_bufsz when the value
+ * exceeds prealloc_bufsz (assuming prealloc_bufsz plus the increment is
+ * less than or equal to UINT_MAX).
+ */
struct comedi_async {
- void *prealloc_buf; /* pre-allocated buffer */
- unsigned int prealloc_bufsz; /* buffer size, in bytes */
- struct comedi_buf_map *buf_map; /* map of buffer pages */
-
- unsigned int max_bufsize; /* maximum buffer size, bytes */
-
- /* byte count for writer (write completed) */
+ void *prealloc_buf;
+ unsigned int prealloc_bufsz;
+ struct comedi_buf_map *buf_map;
+ unsigned int max_bufsize;
unsigned int buf_write_count;
- /* byte count for writer (allocated for writing) */
unsigned int buf_write_alloc_count;
- /* byte count for reader (read completed) */
unsigned int buf_read_count;
- /* byte count for reader (allocated for reading) */
unsigned int buf_read_alloc_count;
-
- unsigned int buf_write_ptr; /* buffer marker for writer */
- unsigned int buf_read_ptr; /* buffer marker for reader */
-
- unsigned int cur_chan; /* useless channel marker for interrupt */
- /* number of bytes that have been received for current scan */
+ unsigned int buf_write_ptr;
+ unsigned int buf_read_ptr;
+ unsigned int cur_chan;
unsigned int scan_progress;
- /* keeps track of where we are in chanlist as for munging */
unsigned int munge_chan;
- /* number of bytes that have been munged */
unsigned int munge_count;
- /* buffer marker for munging */
unsigned int munge_ptr;
-
- unsigned int events; /* events that have occurred */
-
+ unsigned int events;
struct comedi_cmd cmd;
-
wait_queue_head_t wait_head;
-
unsigned int cb_mask;
-
int (*inttrig)(struct comedi_device *dev, struct comedi_subdevice *s,
unsigned int x);
};
--
2.0.0
--
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