If the "read" file operation handler, `comedi_read()` is passed 0 for
the amount to read, some error conditions are currently skipped and the
function just returns 0.  Change it to check those error conditions and
return an error value if appropriate.  The trickiest case is the check
for when the previously set up asynchronous command has terminated with
an error.  In that case, `-EPIPE` is returned (as it is for a read of
non-zero length) and the subdevice gets marked as non-busy.

A zero-length read that returns 0 has no other effects, in particular,
it does not cause the subdevice to be marked as non-busy, and the return
value does not indicate an "end-of-file" condition.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

In order to perform a "read" file operation, an asynchronous COMEDI
command in the "read" direction needs to have been set up by the current
file object on the COMEDI "read" subdevice associated with the file
object.  If there is a "read" subdevice, but a command has not been set
up by the file object (or is has been set-up in the wrong direction),
`comedi_read()` currently returns one of two error values `-EINVAL` or
`-EACCES`.  `-EACCES` is returned if the command was set up by a
different subdevice, or somewhat randomly, if a COMEDI "instruction" is
currently being processed.  `-EINVAL` is returned in other cases.
Simplify it by returning `-EINVAL` for all these cases.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The "read" file operation handler, `comedi_read()` returns an error for
pretty much any condition that prevents a "read" going ahead.  One of
the conditions that prevents a "read" going ahead is that no
asynchronous command has been set up, but that currently results in a
return value of 0 (unless COMEDI instructions are being processed or an
asynchronous command has been set up by a different file object).
Change it to return `-EINVAL` in this case.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

`comedi_read()` initializes `retval` to 0.  The other `retval = 0`
assignments are superfluous, so remove them.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

`comedi_read()` copies data from the acquisition data buffer, which is
cyclic, to the user buffer using a single call to `copy_to_user()`.  It
currently avoids having to deal with wraparound of the cyclic buffer by
limiting the amount it copies (and the amount returned to the user).
Change it to deal with the wraparound using two calls to
`copy_to_user()` if necessary.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

At one point in `comedi_read()`, the variable `n` gets assigned to the
minimum of the parameter `nbytes` and the amount of readable buffer
space `m`.  The way that is done currently is unsafe in the unlikely
case that `nbytes` exceeds `UINT_MAX`, so fix it.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

In `comedi_read()`, the `n` and `m` variables are of type `int`.  Change
them to `unsigned int` as they are used to measure a positive number of
bytes.  The `count` variable is also of type `int` and holds the
returned number of bytes.  Change it to type `ssize_t` to match the
function's return type.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

`comedi_read()` is the handler for the "read" file operation for COMEDI
devices.  It mostly runs without using the main mutex of the COMEDI
device, but uses the `attach_lock` rwsemaphore to protect against the
COMEDI device becoming "detached".  A file object can read data
resulting from a COMEDI asynchonous command if it initiated the command.
The COMEDI subdevice is marked as busy when the command is started.  At
some point, the "read" handler detects that the command has terminated
and all available data has been read and so marks the subdevice as
non-busy.

In order to mark the subdevice as non-busy, the "read" handler needs to
release the `attach_lock` rwsemaphore and `acquire the main `mutex`.
There is a vulnerable point between the two, so it checks that the
device is still attached after acquiring the mutex.  However, it does
not currently check that the conditions for becoming non-busy still
hold.  Add some more checks that the subdevice is still busy with a
command initiated by the same file object, that command is in the correct
direction (in case the subdevice supports both "read" and "write"), that
command has terminated, and has no data available to be read.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

If an asynchronous "read" command is no longer running but the subdevice
is still busy, it becomes non-busy once there is no more data available
in the buffer.  Some or all of the data written to the buffer might not
have been "munged" yet, and it cannot be read until it has been munged
by the writer.  However, since the command is no longer running, we
cannot expect any remaining unmunged data to get munged so we should
ignore it.  Call `comedi_buf_read_n_available()` to check the amount of
munged data available to be read, replacing the call to
`comedi_buf_n_bytes_ready()` which checked the amount of written (but
possibly not yet munged) data available to be read.  This affects both
the "read" file operation (done in `comedi_read()`) and the
`COMEDI_BUFINFO` ioctl handling (done in `do_bufinfo_ioctl()`).  (The
latter is used when data is transferred directly through the mmapped
buffer instead of via the "read" file operation.)
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

If a COMEDI subdevice is busy handling an asynchronous command in the
"read" direction, then after the command has terminated itself, the
"read" file operation handler, `comedi_read()` should keep the subdevice
busy until all available data has been read and it has returned 0 to
indicate an "end-of-file" condition.  Currently, it has a bug where it
can mark the subdevice as non-busy even when returning a non-zero count.
The bug is slightly hidden because the next "read" will return 0 because
the subdevice is no longer busy.  Fix it by checking the return count is
0 before deciding to mark the subdevice as non-busy.

The call to `comedi_is_subdevice_idle()` is superfluous as the
`become_nonbusy` variable will have been set to `true` when considering
becoming non-busy.  Strictly speaking, checking the return count is
superfluous too, as `become_nonbusy` doesn't get set to `true` unless
the count is 0, but check the return count anyway to make the intention
clearer.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The main mutex in a comedi device can get held for quite a while when
processing comedi instructions, so for performance reasons, the "read"
and "write" file operations do not use it; they use use the
`attach_lock` rwsemaphore to protect against the comedi device becoming
detached at an inopportune moment.  Do the same for the "poll" file
operation.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Currently, the "poll" file operation checks if an asynchronous "read"
(or "write" command is active on the "read" (or "write" subdevice, but
does not consider whether the command was started from the file object
being polled.  Since that is the only file object able to read (or
write) data, take it into consideration.

With this change, if no read (or write) command is running on the
subdevice, or it is started by a different file object, the file object
is marked as readable (or writeable) regardless, but the read (or write)
file operation will return an error.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

When handling the "poll" file operation and checking for `POLLOUT`,
don't allocate space from the buffer for writing, just check that space
is available for writing.  That check is done after checking that an
asynchronous "write" command is running on the subdevice.  Allocating
the buffer space before checking a "write" command is running can cause
problems if the subdevice supports commands in either direction and
currently has an active "read" command.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Add a new function `comedi_buf_write_n_available()` to return the amount
of buffer space available for writing, including space already allocated
by `comedi_buf_write_alloc()` plus any unallocated space available.
This is currently just for internal use by the comedi core, so is not
exported.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Rename the local function `comedi_buf_write_n_available()` to
`comedi_buf_write_n_unalloc()`.  It is the amount of unallocated space
available in the buffer that is available to be allocated for writing
and does not include the space that has already been allocated for
writing.  This is unlike the exported function
`comedi_buf_read_n_available()` which includes the space available to be
allocated for reading plus the space already allocated for reading.  The
new name breaks the unintentional naming symmetry (and also clears the
way for the old name to be reused for a new function).
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Comedi subdevices that support asynchronous acquisition commands have a
wait queue head used for blocking reads or writes and for the poll file
operation.  The comedi device may have several subdevices that support
"read" and/or "write" commands, but each open file object has at most
one "read" subdevice and one "write" subdevice.  It's possible (though
rare) for those to be the same subdevice if the subdevice supports
commands in either direction.  In that case, the "poll" file operation
doesn't really need to do a `poll_wait()` on the same subdevice twice.
Although harmless, it wastes a poll table entry.  Check for that, and
avoid it.
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

For aesthetics, rename these private data members to match the registers
they are associated with.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

For aesthetics, move this comment to follow the format of the other
subdevices.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The PC-CARD DAS16/16-AO board only has 4 digital I/O channels. The other
boards supported by this driver have 8. Add the boardinfo to correctly
initialize the subdevice.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The hardware has an 8254 counter/timer to provide a pacer clock using
counters 1 and 2. Counter 0 is available to the user.

Hook up the subdevice support to allow the user to use counter 0.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This driver currently code not support async commands. Remove the
SDF_CMD_READ subdev_flag and len_chanlist initialization from the
subdevice init.

For aesthetics, rename the (*insn_read) function.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Only one of the boards supported by this driver has analog outputs.
For aesthetics, change the 'n_ao_chans' member of the boardinfo into
a bit-field flag 'has_ao'.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Define the bits in these registers and use them to remove the "magic"
values in the driver.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The ai mux register is used program the hi/lo channels in a scan.
According to the user manual, the hi and lo channels should be
the same  to sample one channel.

Introduce some macros to set the appropriate bits in the ai mux
register and fix the ai (*insn_read).
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

For aesthetics, add _REG to all the register map offsets and convert
the values to hex.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Reformat the multi-line comments in the kernel CodingStyle.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

For aesthetics, move and reword the comment to follow the format of
the other subdevices.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
CC: Ian Abbott <abbotti@mev.co.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This board name is incorrect. The proper name is 104-AO12-4.

Change the boardinfo name to 'aio_aio12_4' to follow the format of
the other boardtypes.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This driver supports three board types with these differences:
  104-AIO12-8 - eight 12-bit analog in, four 12-bit analog out
  104-AI12-8  - eight 12-bit analog in
  104-AO12-4  - four 12-bit analog out

Convert the boardinfo 'ai_nchan' and 'ao_nchan' into bit-field
flags 'has_ai' and 'has_ao' so save a bit of space.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

According to the user manual, analog input bipolar data is 2's
complement and unipolar is straight binry. Use the core helpers
to munge the data appropriately.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The analog outputs are all single-ended. Remove the SDF_DIFF
subdev_flag from the subdevice initialization.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

For aesthetics, move the comedi_lrange definition used in this driver
to the follow the norm in comedi drivers and rename the variable.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This board has an industry-standard 8254 chip with the gate, clock,
and output pins for each counter available on the connector.

Hookup the 8254 counter as a comedi subdevice.

Provice an (*insn_config) for the user to query the clock source
for each channel.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Change the MODULE_DESCRIPTION to something more useful than the
generic "Comedi low-level driver".
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Reformat the multi-line comments in the kernel CodingStyle.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

As suggested by checkpatch.pl, use the BIT macro to define the
register bits.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Rename thie CamelCase member of the private data. Add a comment in
the interrupt handler to clarify why the channel interval is updated
again.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

The PCI-1720 board is supported by this driver but uses a different
register map. For aesthetics, rename the defines to match the
PCI171X_* format.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Rename these CamelCase defines.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Rename the CamelCase and use the BIT macro to define the bits.
Also, rename the associated CamelCase members of the private data.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>