staging: comedi: cb_pcidas64: Use insn->n in EEPROM insn_read handler

The `insn_read` handler for the EEPROM subdevice (`eeprom_insn_read()`)
currently ignores `insn->n` (the number of samples to be read) and
assumes a single sample is to be read.  But `insn->n` could be 0,
meaning no samples should be read, in which case `data[0]` ought not to
be written.  (The comedi core at least ensures that `data[0]` exists,
but we should not rely on that.)

Follow the usual Comedi guidelines and interpret `insn->n` as the number
of samples to be read, but only read the EEPROM location once and make
`insn->n` copies, as we don't expect the contents of the EEPROM location
to change between readings.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 10 insertions, 2 deletions

diff --git a/drivers/staging/comedi/drivers/cb_pcidas64.c b/drivers/staging/comedi/drivers/cb_pcidas64.c
index 44e5aaf8bae5..e1774e09a320 100644
--- a/drivers/staging/comedi/drivers/cb_pcidas64.c
+++ b/drivers/staging/comedi/drivers/cb_pcidas64.c
@@ -3768,9 +3768,17 @@ static int eeprom_read_insn(struct comedi_device *dev,
 			    struct comedi_subdevice *s,
 			    struct comedi_insn *insn, unsigned int *data)
 {
-	data[0] = read_eeprom(dev, CR_CHAN(insn->chanspec));
+	unsigned int val;
+	unsigned int i;
 
-	return 1;
+	if (insn->n) {
+		/* No point reading the same EEPROM location more than once. */
+		val = read_eeprom(dev, CR_CHAN(insn->chanspec));
+		for (i = 0; i < insn->n; i++)
+			data[i] = val;
+	}
+
+	return insn->n;
 }
 
 /* Allocate and initialize the subdevice structures. */