staging: comedi: cb_pcidas: Allow 2-channel commands for AO subdevice

The "cb_pcidas" driver supports asynchronous commands on the analog
output (AO) subdevice for those boards that have an AO FIFO.  The code
(in `cb_pcidas_ao_check_chanlist()` and `cb_pcidas_ao_cmd()`) to
validate and set up the command supports output to a single channel or
to two channels simultaneously (the boards have two AO channels).
However, the code in `cb_pcidas_auto_attach()` that initializes the
subdevices neglects to initialize the AO subdevice's `len_chanlist`
member, leaving it set to 0, but the Comedi core will "correct" it to 1
if the driver neglected to set it.  This limits commands to use a single
channel (either channel 0 or 1), but the limit should be two channels.
Set the AO subdevice's `len_chanlist` member to be the same value as the
`n_chan` member, which will be 2.

Cc: <stable@vger.kernel.org>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20201021122142.81628-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/cb_pcidas.c b/drivers/staging/comedi/drivers/cb_pcidas.c
index 48ec2ee..d740c47 100644 (file)
--- a/drivers/staging/comedi/drivers/cb_pcidas.c
+++ b/drivers/staging/comedi/drivers/cb_pcidas.c
@@ -1342,6 +1342,7 @@ static int cb_pcidas_auto_attach(struct comedi_device *dev,
                if (dev->irq && board->has_ao_fifo) {
                        dev->write_subdev = s;
                        s->subdev_flags |= SDF_CMD_WRITE;
+                       s->len_chanlist = s->n_chan;
                        s->do_cmdtest   = cb_pcidas_ao_cmdtest;
                        s->do_cmd       = cb_pcidas_ao_cmd;
                        s->cancel       = cb_pcidas_ao_cancel;