On Sun, 2018-11-18 at 02:25 -0200, Matheus Tavares wrote:
> From: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
I think you can use "Suggested-by:" instead.
But this is also fine.
> Signed-off-by: Matheus Tavares <matheus.bernardino@xxxxxx>
> ---
> 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;
