On Sat, 21 Dec 2024 17:56:00 +0200
Alisa-Dariana Roman <alisadariana@xxxxxxxxx> wrote:
> Some sigma-delta ADCs, such as AD7191 and AD7780, have no registers and
> start conversion when CS is asserted. Add helper function to support
> this use case by allowing devices to assert CS without performing
> register operations.
Hi Alisa-Dariana,
I had a look at the ad7191 datasheet. Given this description,
I was expecting to see it do a pre pulse of the chip select to trigger
the acquisition. However, what I see is a power down line (which is more
or less a chip select) but it just has a specified t1 delay before the
DOUT will change to the state for the first bit and the host
can start driving the clock.
That can be done by setting spi_device->cs_setup to whatever delay is
needed. The text is spi_device docs are a little vague,
but I'd take it as t1 + t2 (maybe t3 to be safe).
That is going to be more reliable than trying to hold the cs across
messages / spi_sync() calls, particularly if the bus might not be
locked (which the code below suggests).
Jonathan
>
> This function can be used by drivers through their set_mode callback.
>
> Signed-off-by: Alisa-Dariana Roman <alisa.roman@xxxxxxxxxx>
> ---
> drivers/iio/adc/ad_sigma_delta.c | 24 ++++++++++++++++++++++++
> include/linux/iio/adc/ad_sigma_delta.h | 1 +
> 2 files changed, 25 insertions(+)
>
> diff --git a/drivers/iio/adc/ad_sigma_delta.c b/drivers/iio/adc/ad_sigma_delta.c
> index 0f355dac7813..c0f33d4baddf 100644
> --- a/drivers/iio/adc/ad_sigma_delta.c
> +++ b/drivers/iio/adc/ad_sigma_delta.c
> @@ -48,6 +48,30 @@ void ad_sd_set_comm(struct ad_sigma_delta *sigma_delta, uint8_t comm)
> }
> EXPORT_SYMBOL_NS_GPL(ad_sd_set_comm, "IIO_AD_SIGMA_DELTA");
>
> +/**
> + * ad_sd_assert_cs() - Assert chip select line
> + *
> + * @sigma_delta: The sigma delta device
> + *
> + * Returns 0 on success, an error code otherwise.
> + **/
> +int ad_sd_assert_cs(struct ad_sigma_delta *sigma_delta)
> +{
> + struct spi_transfer t = {
> + .len = 0,
> + .cs_change = sigma_delta->keep_cs_asserted,
> + };
> + struct spi_message m;
> +
> + spi_message_init(&m);
> + spi_message_add_tail(&t, &m);
> +
> + if (sigma_delta->bus_locked)
> + return spi_sync_locked(sigma_delta->spi, &m);
> + return spi_sync(sigma_delta->spi, &m);
> +}
> +EXPORT_SYMBOL_NS_GPL(ad_sd_assert_cs, IIO_AD_SIGMA_DELTA);
> +
> /**
> * ad_sd_write_reg() - Write a register
> *
> diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
> index 417073c52380..99ab56d04793 100644
> --- a/include/linux/iio/adc/ad_sigma_delta.h
> +++ b/include/linux/iio/adc/ad_sigma_delta.h
> @@ -178,6 +178,7 @@ static inline int ad_sigma_delta_postprocess_sample(struct ad_sigma_delta *sd,
> }
>
> void ad_sd_set_comm(struct ad_sigma_delta *sigma_delta, uint8_t comm);
> +int ad_sd_assert_cs(struct ad_sigma_delta *sigma_delta);
> int ad_sd_write_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
> unsigned int size, unsigned int val);
> int ad_sd_read_reg(struct ad_sigma_delta *sigma_delta, unsigned int reg,
