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    Subject[PATCH 5.4 355/453] staging: comedi: mf6x4: Fix AI end-of-conversion detection
    Date
    From: Ian Abbott <abbotti@mev.co.uk>

    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>

    ---
    drivers/staging/comedi/drivers/mf6x4.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/drivers/staging/comedi/drivers/mf6x4.c
    +++ b/drivers/staging/comedi/drivers/mf6x4.c
    @@ -112,8 +112,9 @@ static int mf6x4_ai_eoc(struct comedi_de
    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;
    }

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