staging: comedi: mf6x4: Fix AI end-of-conversion detection

commit 56c90457ebfe9422496aac6ef3d3f0f0ea8b2ec2 upstream.

I have had reports from two different people that attempts to read the
analog input channels of the MF624 board fail with an `ETIMEDOUT` error.

After triggering the conversion, the code calls `comedi_timeout()` with
`mf6x4_ai_eoc()` as the callback function to check if the conversion is
complete.  The callback returns 0 if complete or `-EBUSY` if not yet
complete.  `comedi_timeout()` returns `-ETIMEDOUT` if it has not
completed within a timeout period which is propagated as an error to the
user application.

The existing code considers the conversion to be complete when the EOLC
bit is high.  However, according to the user manuals for the MF624 and
MF634 boards, this test is incorrect because EOLC is an active low
signal that goes high when the conversion is triggered, and goes low
when the conversion is complete.  Fix the problem by inverting the test
of the EOLC bit state.

Fixes: 04b565021a83 ("comedi: Humusoft MF634 and MF624 DAQ cards driver")
Cc: <stable@vger.kernel.org> # v4.4+
Cc: Rostislav Lisovy <lisovy@gmail.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20201207145806.4046-1-abbotti@mev.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/mf6x4.c b/drivers/staging/comedi/drivers/mf6x4.c
index fbdf181d8ccccc228c131346a9e9ec9dc403d11b..40aa24a9b2c30616ec5eec77032ab5fc5a626e48 100644 (file)
--- a/drivers/staging/comedi/drivers/mf6x4.c
+++ b/drivers/staging/comedi/drivers/mf6x4.c
@@ -121,8 +121,9 @@ static int mf6x4_ai_eoc(struct comedi_device *dev,
        struct mf6x4_private *devpriv = dev->private;
        unsigned int status;
 
+       /* EOLC goes low at end of conversion. */
        status = ioread32(devpriv->gpioc_reg);
-       if (status & MF6X4_GPIOC_EOLC)
+       if ((status & MF6X4_GPIOC_EOLC) == 0)
                return 0;
        return -EBUSY;
 }