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    SubjectRe: [PATCH v2 3/7] staging:iio:ad2s90: Add max frequency check at probe
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    On Sun, 2018-11-18 at 02:25 -0200, Matheus Tavares wrote:
    > From: Alexandru Ardelean <alexandru.ardelean@analog.com>
    >
    > This patch adds a max frequency check at the beginning of ad2s90_probe
    > function so that when it is set to a value above 0.83Mhz, dev_err is
    > called with an appropriate message and -EINVAL is returned.
    >
    > The defined limit is 0.83Mhz instead of 2Mhz, which is the chip's max
    > frequency as specified in the datasheet, because, as also specified in
    > the datasheet, a 600ns delay is expected between the application of a
    > logic LO to CS and the application of SCLK. Since the delay is not
    > implemented in the spi code, to satisfy it, SCLK's period should be at
    > most 2 * 600ns, so the max frequency should be 1 / (2 * 6e-7), which
    > gives roughly 830000Hz.
    >
    > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>

    I think you can use "Suggested-by:" instead.
    But this is also fine.

    > Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
    > ---
    > Changes in v2:
    > - Correctly credit Alexandru as the patch's author
    >
    > drivers/staging/iio/resolver/ad2s90.c | 12 ++++++++++++
    > 1 file changed, 12 insertions(+)
    >
    > diff --git a/drivers/staging/iio/resolver/ad2s90.c
    > b/drivers/staging/iio/resolver/ad2s90.c
    > index 913d6fad2d4d..fe90f2056bff 100644
    > --- a/drivers/staging/iio/resolver/ad2s90.c
    > +++ b/drivers/staging/iio/resolver/ad2s90.c
    > @@ -19,6 +19,12 @@
    > #include <linux/iio/iio.h>
    > #include <linux/iio/sysfs.h>
    >
    > +/*
    > + * Although chip's max frequency is 2Mhz, it needs 600ns between CS and
    > the
    > + * first falling edge of SCLK, so frequency should be at most 1 / (2 *
    > 6e-7)
    > + */
    > +#define AD2S90_MAX_SPI_FREQ_HZ 830000
    > +
    > struct ad2s90_state {
    > struct mutex lock;
    > struct spi_device *sdev;
    > @@ -78,6 +84,12 @@ static int ad2s90_probe(struct spi_device *spi)
    > struct iio_dev *indio_dev;
    > struct ad2s90_state *st;
    >
    > + if (spi->max_speed_hz > AD2S90_MAX_SPI_FREQ_HZ) {
    > + dev_err(&spi->dev, "SPI CLK, %d Hz exceeds %d Hz\n",
    > + spi->max_speed_hz, AD2S90_MAX_SPI_FREQ_HZ);
    > + return -EINVAL;
    > + }
    > +
    > indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
    > if (!indio_dev)
    > return -ENOMEM;
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