Re: [PATCH v8 14/17] iio: adc: ad4695: Add support for SPI offload

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 10 Feb 2025 10:01:57 -0600
David Lechner <dlechner@baylibre.com> wrote:

> On 2/7/25 2:09 PM, David Lechner wrote:
> > Add support for SPI offload to the ad4695 driver. SPI offload allows
> > sampling data at the max sample rate (500kSPS or 1MSPS).
> > 
> > This is developed and tested against the ADI example FPGA design for
> > this family of ADCs [1].
> > 
> > [1]: http://analogdevicesinc.github.io/hdl/projects/ad469x_fmc/index.html
> > 
> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > Reviewed-by: Nuno Sa <nuno.sa@analog.com>
> > Signed-off-by: David Lechner <dlechner@baylibre.com>
> > ---
> >   
> 
> ...
> 
> > ---
> >  drivers/iio/adc/Kconfig  |   1 +
> >  drivers/iio/adc/ad4695.c | 445 +++++++++++++++++++++++++++++++++++++++++++++--
> >  2 files changed, 429 insertions(+), 17 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> > index 995b9cacbaa964d26424346120c139858f93cdcd..ec60b64c46e187e2be18ab1f8ca9e6f4f03299f9 100644
> > --- a/drivers/iio/adc/Kconfig
> > +++ b/drivers/iio/adc/Kconfig
> > @@ -52,6 +52,7 @@ config AD4695
> >  	tristate "Analog Device AD4695 ADC Driver"
> >  	depends on SPI
> >  	select IIO_BUFFER
> > +	select IIO_BUFFER_DMAENGINE
> >  	select IIO_TRIGGERED_BUFFER
> >  	select REGMAP  
> 
> I missed adding
> 
> 	select SPI_OFFLOAD
> 
> Closes: https://lore.kernel.org/oe-kbuild-all/202502090910.ganYXEeF-lkp@intel.com/
> 
> >  	help  
> 
Thanks. Fixed up whilst applying.
> ...
> 
> 
> > +static int ad4695_offload_buffer_postenable(struct iio_dev *indio_dev)
> > +{
> > +	struct ad4695_state *st = iio_priv(indio_dev);
> > +	struct spi_offload_trigger_config config = {
> > +		.type = SPI_OFFLOAD_TRIGGER_DATA_READY,
> > +	};
> > +	struct spi_transfer *xfer = &st->buf_read_xfer[0];
> > +	struct pwm_state state;
> > +	u8 temp_chan_bit = st->chip_info->num_voltage_inputs;
> > +	u8 num_slots = 0;
> > +	u8 temp_en = 0;
> > +	unsigned int bit;
> > +	int ret;
> > +
> > +	iio_for_each_active_channel(indio_dev, bit) {
> > +		if (bit == temp_chan_bit) {
> > +			temp_en = 1;
> > +			continue;
> > +		}
> > +
> > +		ret = regmap_write(st->regmap, AD4695_REG_AS_SLOT(num_slots),
> > +				   FIELD_PREP(AD4695_REG_AS_SLOT_INX, bit));
> > +		if (ret)
> > +			return ret;
> > +
> > +		num_slots++;
> > +	}
> > +
> > +	/*
> > +	 * For non-offload, we could discard data to work around this
> > +	 * restriction, but with offload, that is not possible.
> > +	 */
> > +	if (num_slots < 2) {
> > +		dev_err(&st->spi->dev,
> > +			"At least two voltage channels must be enabled.\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	ret = regmap_update_bits(st->regmap, AD4695_REG_TEMP_CTRL,
> > +				 AD4695_REG_TEMP_CTRL_TEMP_EN,
> > +				 FIELD_PREP(AD4695_REG_TEMP_CTRL_TEMP_EN,
> > +					    temp_en));
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* Each BUSY event means just one sample for one channel is ready. */
> > +	memset(xfer, 0, sizeof(*xfer));
> > +	xfer->offload_flags = SPI_OFFLOAD_XFER_RX_STREAM;
> > +	/* Using 19 bits per word to allow for possible oversampling */
> > +	xfer->bits_per_word = 19;
> > +	xfer->len = 4;
> > +
> > +	spi_message_init_with_transfers(&st->buf_read_msg, xfer, 1);
> > +	st->buf_read_msg.offload = st->offload;
> > +
> > +	ret = spi_optimize_message(st->spi, &st->buf_read_msg);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/*
> > +	 * NB: technically, this is part the SPI offload trigger enable, but it
> > +	 * doesn't work to call it from the offload trigger enable callback
> > +	 * because it requires accessing the SPI bus. Calling it from the
> > +	 * trigger enable callback could cause a deadlock.
> > +	 */
> > +	ret = regmap_set_bits(st->regmap, AD4695_REG_GP_MODE,
> > +			      AD4695_REG_GP_MODE_BUSY_GP_EN);
> > +	if (ret)
> > +		goto err_unoptimize_message;
> > +
> > +	ret = spi_offload_trigger_enable(st->offload, st->offload_trigger,
> > +					 &config);
> > +	if (ret)
> > +		goto err_disable_busy_output;
> > +
> > +	ret = ad4695_enter_advanced_sequencer_mode(st, num_slots);
> > +	if (ret)
> > +		goto err_offload_trigger_disable;
> > +
> > +	guard(mutex)(&st->cnv_pwm_lock);  
> 
> Apparently clang doesn't like this guard() after goto, so I'll have to figure
> out what to do about that. Probably need to add a helper function to avoid
> goto below from jumping out of scoped_guard().
> 
> https://lore.kernel.org/oe-kbuild-all/202502090806.KxEvxCZC-lkp@intel.com/

Easiest option don't use guard(). Sometimes they are not the right choice!

diff --git a/drivers/iio/adc/ad4695.c b/drivers/iio/adc/ad4695.c
index d73d2ff77625..d1e7634001b3 100644
--- a/drivers/iio/adc/ad4695.c
+++ b/drivers/iio/adc/ad4695.c
@@ -800,7 +800,7 @@ static int ad4695_offload_buffer_postenable(struct iio_dev *indio_dev)
        if (ret)
                goto err_offload_trigger_disable;
 
-       guard(mutex)(&st->cnv_pwm_lock);
+       mutex_lock(&st->cnv_pwm_lock);
        pwm_get_state(st->cnv_pwm, &state);
        /*
         * PWM subsystem generally rounds down, so requesting 2x minimum high
@@ -808,6 +808,7 @@ static int ad4695_offload_buffer_postenable(struct iio_dev *indio_dev)
         */
        state.duty_cycle = AD4695_T_CNVH_NS * 2;
        ret = pwm_apply_might_sleep(st->cnv_pwm, &state);
+       mutex_unlock(st->cnv_pwm_lock);
        if (ret)
                goto err_offload_exit_conversion_mode;


For now I've applied this as I want to get some build testing on this series,  but
feel free to send a patch to tweak this to a different solution.

Jonathan

> 
> > +	pwm_get_state(st->cnv_pwm, &state);
> > +	/*
> > +	 * PWM subsystem generally rounds down, so requesting 2x minimum high
> > +	 * time ensures that we meet the minimum high time in any case.
> > +	 */
> > +	state.duty_cycle = AD4695_T_CNVH_NS * 2;
> > +	ret = pwm_apply_might_sleep(st->cnv_pwm, &state);
> > +	if (ret)
> > +		goto err_offload_exit_conversion_mode;
> > +
> > +	return 0;
> > +
> > +err_offload_exit_conversion_mode:
> > +	/*
> > +	 * We have to unwind in a different order to avoid triggering offload.
> > +	 * ad4695_exit_conversion_mode() triggers a conversion, so it has to be
> > +	 * done after spi_offload_trigger_disable().
> > +	 */
> > +	spi_offload_trigger_disable(st->offload, st->offload_trigger);
> > +	ad4695_exit_conversion_mode(st);
> > +	goto err_disable_busy_output;
> > +
> > +err_offload_trigger_disable:
> > +	spi_offload_trigger_disable(st->offload, st->offload_trigger);
> > +
> > +err_disable_busy_output:
> > +	regmap_clear_bits(st->regmap, AD4695_REG_GP_MODE,
> > +			  AD4695_REG_GP_MODE_BUSY_GP_EN);
> > +
> > +err_unoptimize_message:
> > +	spi_unoptimize_message(&st->buf_read_msg);
> > +
> > +	return ret;
> > +}