On Tuesday, October 30, 2018 7:17 AM, Ian Abbott wrote:
> 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 <abbo...@mev.co.uk>
> ---
> drivers/staging/comedi/drivers/cb_pcidas64.c | 12 ++++++++++--
> 1 file 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;
> }
 
Hi Ian,

I realize it's not the "normal" Comedi use, but with the EEPROM I would think 
that if the user
wanted to read more than one sample they would expect to read a block of data 
from the
EEPROM.

Maybe the EEPROM read should be something like:

+       if (insn->n) {
+               unsigned int address = CR_CHAN(insn->chanspec);
+               for (i = 0; i < insn->n; i++) {
+                       val = read_eeprom(dev, address);
+                       data[i] = val;
+                       address++;
+                       if (address >= s->n_chan)
+                               address = 0;
+               }
+       }

Regards,
Hartley

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