On 20/10/14 19:52, H Hartley Sweeten wrote:
A number of drivers currently use comedi_buf_get() to read single samples
from the the async buffer. This works but the drivers have to handle the
COMEDI_CB_BLOCK and COMEDI_CB_EOS events. Converting those drivers to use
comedi_buf_read_samples() moves the handling of those events into the core.
Add a check to comedi_buf_read_samples() so that the single sample is read
from the buffer only if there is a full sample in the buffer. This allows
comedi_buf_read_samples() to mimic the action of comedi_buf_get() with the
added benifit of handling the events.
Even for more than one sample it would be better if
comedi_buf_read_samples() only read a whole number of samples from the
buffer, e.g. by rounding down the value from
comedi_buf_read_n_available(). Then you wouldn't need to treat single
samples as a special case.
Signed-off-by: H Hartley Sweeten <hsweeten@xxxxxxxxxxxxxxxxxxx>
Cc: Ian Abbott <abbotti@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/comedi/comedi_buf.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/staging/comedi/comedi_buf.c b/drivers/staging/comedi/comedi_buf.c
index 4cf02cb..6b6143b 100644
--- a/drivers/staging/comedi/comedi_buf.c
+++ b/drivers/staging/comedi/comedi_buf.c
@@ -564,6 +564,7 @@ unsigned int comedi_buf_read_samples(struct comedi_subdevice *s,
void *data, unsigned int nsamples)
{
unsigned long long nbytes = nsamples * bytes_per_sample(s);
+ unsigned int n = comedi_buf_read_n_available(s);
if (nbytes > s->async->prealloc_bufsz)
nbytes = s->async->prealloc_bufsz;
@@ -571,6 +572,10 @@ unsigned int comedi_buf_read_samples(struct comedi_subdevice *s,
if (nbytes == 0)
return 0;
+ /* single sample reads must return a full sample */
+ if (nsamples == 1 && n < nbytes)
+ return 0;
+
nbytes = comedi_buf_read_alloc(s, nbytes);
comedi_buf_memcpy_from(s, 0, data, nbytes);
comedi_buf_read_free(s, nbytes);
--
-=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@xxxxxxxxx> )=-
-=( Web: http://www.mev.co.uk/ )=-
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