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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: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20210301165757.243065-2-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2021-03-01 16:57:52 +00:00 committed by Greg Kroah-Hartman
parent a0d1a3864c
commit 7a3f3a7005
1 changed files with 39 additions and 0 deletions
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39
drivers/staging/comedi/drivers/dt2814.c
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@ -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]);