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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@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2014-06-20 14:15:04 +01:00 committed by Greg Kroah-Hartman
parent 684ff4f987
commit 55d128bf99
1 changed files with 92 additions and 25 deletions
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117
drivers/staging/comedi/comedidev.h
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@ -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);
};