comedi: comedi_test: add a DIO subdevice

The fake "comedi_test" device currently has two subdevices: an analog
input subdevice, and an analog output subdevice.  To make it a bit more
useful for testing, add a third subdevice for digital I/O.

The new DIO subdevice has 32 channels with each channel individually
programmable as an input or an output.  To add a bit of interaction,
channels 0 to 15 are wired to channels 16 to 31 (0 to 16, 1 to 17,
etc.), and the state of each wire can be read back on both of the
channels connected to it.  The outputs are modelled as NPN open
collector outputs with a pull-up resistor on the wire, so the state of
each wire (and the value read back from each channel connected to it)
will be logic level 1 unless either channel is configured as an output
at logic level 0.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://patch.msgid.link/20251210124455.69131-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/comedi/drivers/comedi_test.c b/drivers/comedi/drivers/comedi_test.c
index 7984950f0f992cdc64b841dd8ed55b9f2ab93845..01aafce20ef816b89be50e78033fc7d56d70e477 100644 (file)
--- a/drivers/comedi/drivers/comedi_test.c
+++ b/drivers/comedi/drivers/comedi_test.c
@@ -692,6 +692,44 @@ static int waveform_ao_insn_config(struct comedi_device *dev,
        return -EINVAL;
 }
 
+static int waveform_dio_insn_bits(struct comedi_device *dev,
+                                 struct comedi_subdevice *s,
+                                 struct comedi_insn *insn,
+                                 unsigned int *data)
+{
+       u32 driven_low;
+       u16 wires;
+
+       /* Update the channel outputs. */
+       comedi_dio_update_state(s, data);
+       /*
+        * We are modelling the outputs as NPN open collector (0 = driven low,
+        * 1 = high impedance), with the lower 16 channels wired to the upper
+        * 16 channels in pairs (0 to 16, 1 to 17, ..., 15 to 31), with a
+        * pull-up resistor on each wire.  When reading back each channel, we
+        * read back the state of the wire to which it is connected.
+        *
+        * The state of each wire and the value read back from both channels
+        * connected to it will be logic 1 unless either channel connected to
+        * the wire is configured as an output in the logic 0 state.
+        */
+       driven_low = s->io_bits & ~s->state;
+       wires = 0xFFFF & ~driven_low & ~(driven_low >> 16);
+       /* Read back the state of the wires for each pair of channels. */
+       data[1] = wires | (wires << 16);
+
+       return insn->n;
+}
+
+static int waveform_dio_insn_config(struct comedi_device *dev,
+                                   struct comedi_subdevice *s,
+                                   struct comedi_insn *insn,
+                                   unsigned int *data)
+{
+       /* configure each channel as input or output individually */
+       return comedi_dio_insn_config(dev, s, insn, data, 0);
+}
+
 static int waveform_common_attach(struct comedi_device *dev,
                                  int amplitude, int period)
 {
@@ -707,7 +745,7 @@ static int waveform_common_attach(struct comedi_device *dev,
        devpriv->wf_amplitude = amplitude;
        devpriv->wf_period = period;
 
-       ret = comedi_alloc_subdevices(dev, 2);
+       ret = comedi_alloc_subdevices(dev, 3);
        if (ret)
                return ret;
 
@@ -746,6 +784,16 @@ static int waveform_common_attach(struct comedi_device *dev,
        for (i = 0; i < s->n_chan; i++)
                devpriv->ao_loopbacks[i] = s->maxdata / 2;
 
+       s = &dev->subdevices[2];
+       /* digital input/output subdevice */
+       s->type = COMEDI_SUBD_DIO;
+       s->subdev_flags = SDF_READABLE | SDF_WRITABLE;
+       s->n_chan = 32;
+       s->maxdata = 1;
+       s->range_table = &range_digital;
+       s->insn_bits = waveform_dio_insn_bits;
+       s->insn_config = waveform_dio_insn_config;
+
        devpriv->dev = dev;
        timer_setup(&devpriv->ai_timer, waveform_ai_timer, 0);
        timer_setup(&devpriv->ao_timer, waveform_ao_timer, 0);