From 7a3f3a7005cba9cfc1a0d50978f3eb7f3094e02f Mon Sep 17 00:00:00 2001 From: Ian Abbott Date: Mon, 1 Mar 2021 16:57:52 +0000 Subject: [PATCH] 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 Link: https://lore.kernel.org/r/20210301165757.243065-2-abbotti@mev.co.uk Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/drivers/dt2814.c | 39 +++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/drivers/staging/comedi/drivers/dt2814.c b/drivers/staging/comedi/drivers/dt2814.c index bd329d7..7e73aa0 100644 --- a/drivers/staging/comedi/drivers/dt2814.c +++ b/drivers/staging/comedi/drivers/dt2814.c @@ -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]); -- 2.7.4