Re: [PATCH v2 6/9] iio: adc: adi-axi-adc: Add support for AD7606 register writing

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 10 Dec 2024 10:46:46 +0000
Guillaume Stols <gstols@baylibre.com> wrote:

> Since we must access the bus parallel bus using a custom procedure,
> let's add a specialized compatible, and define specialized callbacks for
> writing the registers using the parallel interface.
> 
> Signed-off-by: Guillaume Stols <gstols@baylibre.com>
Hi Guillaume,

A few comments inline.

Thanks,

Jonathan
> ---
>  drivers/iio/adc/ad7606_bi.h   |  16 +++++++
>  drivers/iio/adc/adi-axi-adc.c | 100 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 116 insertions(+)
> 
> diff --git a/drivers/iio/adc/ad7606_bi.h b/drivers/iio/adc/ad7606_bi.h
> new file mode 100644
> index 000000000000..9ade23ec61dd
> --- /dev/null
> +++ b/drivers/iio/adc/ad7606_bi.h

Why bi?  Bus interface?  I'd spell it out.  Header name lengths don't
usually need to be quite this short.

> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Copyright (c) 2010-2024 Analog Devices Inc.
> + * Copyright (c) 2024 Baylibre, SAS
> + */
> +#ifndef __LINUX_PLATFORM_DATA_AD7606_H__
> +#define __LINUX_PLATFORM_DATA_AD7606_H__
> +
> +#include <linux/iio/backend.h>
Only a pointer type needed, so a forward def better than an include
(which costs some trivial amount of compile time).

struct iio_backend;

> +
> +struct ad7606_platform_data {
> +	int (*bus_reg_read)(struct iio_backend *back, u32 reg, u32 *val);
> +	int (*bus_reg_write)(struct iio_backend *back, u32 reg, u32 val);
> +};
> +
> +#endif /* __LINUX_PLATFORM_DATA_AD7606_H__ */
> diff --git a/drivers/iio/adc/adi-axi-adc.c b/drivers/iio/adc/adi-axi-adc.c
> index 7ff636643e56..b8bcf89417b0 100644
> --- a/drivers/iio/adc/adi-axi-adc.c
> +++ b/drivers/iio/adc/adi-axi-adc.c
> @@ -27,6 +27,7 @@
>  #include <linux/iio/buffer.h>
>  #include <linux/iio/iio.h>
>  
> +#include "ad7606_bi.h"
>  /*
>   * Register definitions:
>   *   https://wiki.analog.com/resources/fpga/docs/axi_adc_ip#register_map
> @@ -73,6 +74,12 @@
>  #define ADI_AXI_ADC_REG_DELAY(l)		(0x0800 + (l) * 0x4)
>  #define   AXI_ADC_DELAY_CTRL_MASK		GENMASK(4, 0)
>  
> +#define ADI_AXI_REG_CONFIG_WR			0x0080
> +#define ADI_AXI_REG_CONFIG_RD			0x0084
> +#define ADI_AXI_REG_CONFIG_CTRL			0x008c
> +#define   ADI_AXI_REG_CONFIG_CTRL_READ		0x03
> +#define   ADI_AXI_REG_CONFIG_CTRL_WRITE		0x01
> +
>  #define ADI_AXI_ADC_MAX_IO_NUM_LANES		15
>  
>  #define ADI_AXI_REG_CHAN_CTRL_DEFAULTS		\
> @@ -80,6 +87,11 @@
>  	 ADI_AXI_REG_CHAN_CTRL_FMT_EN |		\
>  	 ADI_AXI_REG_CHAN_CTRL_ENABLE)
>  
> +/* AD7606's specific */
> +#define AD7606_REG_READ_BIT			0x8000
> +#define AD7606_REG_ADDRESS_MASK			0xff00
> +#define AD7606_REG_VALUE_MASK			0x00ff
> +

Maybe name these to keep the ADI_AXI_ prefix as well.  Otherwise it might get
a little confusing wrt to registers in teh deivce.  They are nice short
names currently so that shouldn't make the code to messy.

>  struct axi_adc_info {
>  	unsigned int version;
>  	const struct iio_backend_info *backend_info;
> @@ -313,6 +325,80 @@ static struct iio_buffer *axi_adc_request_buffer(struct iio_backend *back,
>  	return iio_dmaengine_buffer_setup(st->dev, indio_dev, dma_name);
>  }
>  
> +static int axi_adc_raw_write(struct iio_backend *back, void *buf, unsigned int len)
> +{
> +	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
> +	u32 data;
> +	u32 *bdata = buf;

	data = *(u32)(buf);

Is fine here I think rather than the extra local variable that is just
used to do the type cast.

> +
> +	data = *bdata;
> +	regmap_write(st->regmap, ADI_AXI_REG_CONFIG_WR, data);
> +	regmap_write(st->regmap, ADI_AXI_REG_CONFIG_CTRL,
> +		     ADI_AXI_REG_CONFIG_CTRL_WRITE);
> +	usleep_range(50, 100);
> +	regmap_write(st->regmap, ADI_AXI_REG_CONFIG_CTRL, 0x00);
> +	usleep_range(50, 100);
> +
> +	return 0;
> +}

...

> +
> +static int ad7606_bi_reg_write(struct iio_backend *back, u32 reg, u32 val)
> +{
> +	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
> +	u32 buf;
> +
> +	guard(mutex)(&st->lock);
> +
> +	/* Read any register to switch to register mode */

What follows looks like a write...

> +	buf = 0xaf00;
> +	axi_adc_raw_write(back, &buf, sizeof(buf));
> +
> +	buf = FIELD_PREP(AD7606_REG_ADDRESS_MASK, reg) | FIELD_PREP(AD7606_REG_VALUE_MASK, val);
> +	axi_adc_raw_write(back, &buf, sizeof(buf));
> +
> +	/* Write 0x0 on the bus to get back to ADC mode */
> +	buf = 0;
> +	axi_adc_raw_write(back, &buf, sizeof(buf));
> +
> +	return 0;
> +}