Commit 7a3f3a70 authored by Ian Abbott's avatar Ian Abbott Committed by Greg Kroah-Hartman
Browse files

staging: comedi: dt2814: Clear stale AI data before operation 



When performing a Comedi read instruction or setting up an asynchronous
command on the AI subdevice, clear any stale data on the A/D registers
by waiting for the Status register's BUSY bit to clear (if set) and then
if the FINISH or ERR bit is set, reading the A/D Data register twice to
clear the stale data.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20210301165757.243065-2-abbotti@mev.co.uk


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a0d1a386

drivers/staging/comedi/drivers/dt2814.c

+39 −0
Original line number Diff line number Diff line
@@ -52,6 +52,43 @@ struct dt2814_private { 
#define DT2814_TIMEOUT 10

#define DT2814_MAX_SPEED 100000	/* Arbitrary 10 khz limit */



static int dt2814_ai_notbusy(struct comedi_device *dev,

			     struct comedi_subdevice *s,

			     struct comedi_insn *insn,

			     unsigned long context)

{

	unsigned int status;



	status = inb(dev->iobase + DT2814_CSR);

	if (context)

		*(unsigned int *)context = status;

	if (status & DT2814_BUSY)

		return -EBUSY;

	return 0;

}



static int dt2814_ai_clear(struct comedi_device *dev)

{

	unsigned int status = 0;

	int ret;



	/* Wait until not busy and get status register value. */

	ret = comedi_timeout(dev, NULL, NULL, dt2814_ai_notbusy,

			     (unsigned long)&status);

	if (ret)

		return ret;



	if (status & (DT2814_FINISH | DT2814_ERR)) {

		/*

		 * There unread data, or the error flag is set.

		 * Read the data register twice to clear the condition.

		 */

		inb(dev->iobase + DT2814_DATA);

		inb(dev->iobase + DT2814_DATA);

	}

	return 0;

}



static int dt2814_ai_eoc(struct comedi_device *dev,

			 struct comedi_subdevice *s,

			 struct comedi_insn *insn,
@@ -73,6 +110,7 @@ static int dt2814_ai_insn_read(struct comedi_device *dev, 
	int chan;

	int ret;



	dt2814_ai_clear(dev);	/* clear stale data or error */

	for (n = 0; n < insn->n; n++) {

		chan = CR_CHAN(insn->chanspec);
@@ -174,6 +212,7 @@ static int dt2814_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s) 
	int chan;

	int trigvar;



	dt2814_ai_clear(dev);	/* clear stale data or error */

	trigvar = dt2814_ns_to_timer(&cmd->scan_begin_arg, cmd->flags);



	chan = CR_CHAN(cmd->chanlist[0]);