linux-kernel - Re: [PATCH v10 5/8] iio: adc: adi-axi-adc: set data format

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Message-ID: <c7778b8d-abaa-47b7-834b-e62c30f6b8d9@baylibre.com>
Date: Fri, 17 Jan 2025 11:50:21 -0600
From: David Lechner <dlechner@...libre.com>
To: Nuno Sá <noname.nuno@...il.com>,
 Antoniu Miclaus <antoniu.miclaus@...log.com>, jic23@...nel.org,
 robh@...nel.org, conor+dt@...nel.org, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-pwm@...r.kernel.org
Subject: Re: [PATCH v10 5/8] iio: adc: adi-axi-adc: set data format

On 1/17/25 10:20 AM, Nuno Sá wrote:
> On Fri, 2025-01-17 at 15:06 +0200, Antoniu Miclaus wrote:
>> Add support for selecting the data format within the AXI ADC ip.
>>
>> Signed-off-by: Antoniu Miclaus <antoniu.miclaus@...log.com>
>> ---
> 
> Reviewed-by: Nuno Sa <nuno.sa@...log.com>
> 
>> no changes in v10.
>>  drivers/iio/adc/adi-axi-adc.c | 46 +++++++++++++++++++++++++++++++++++
>>  1 file changed, 46 insertions(+)
>>
>> diff --git a/drivers/iio/adc/adi-axi-adc.c b/drivers/iio/adc/adi-axi-adc.c
>> index d2e1dc63775c..3c213ca5ff8e 100644
>> --- a/drivers/iio/adc/adi-axi-adc.c
>> +++ b/drivers/iio/adc/adi-axi-adc.c
>> @@ -45,6 +45,12 @@
>>  #define ADI_AXI_ADC_REG_CTRL			0x0044
>>  #define    ADI_AXI_ADC_CTRL_DDR_EDGESEL_MASK	BIT(1)
>>  
>> +#define ADI_AXI_ADC_REG_CNTRL_3			0x004c
>> +#define   AD485X_CNTRL_3_PACKET_FORMAT_MSK	GENMASK(1, 0)
>> +#define   AD485X_PACKET_FORMAT_20BIT		0x0
>> +#define   AD485X_PACKET_FORMAT_24BIT		0x1
>> +#define   AD485X_PACKET_FORMAT_32BIT		0x2
>> +
>>  #define ADI_AXI_ADC_REG_DRP_STATUS		0x0074
>>  #define   ADI_AXI_ADC_DRP_LOCKED		BIT(17)
>>  
>> @@ -312,6 +318,45 @@ static int axi_adc_interface_type_get(struct iio_backend
>> *back,
>>  	return 0;
>>  }
>>  
>> +static int axi_adc_data_size_set(struct iio_backend *back, unsigned int size)
>> +{
>> +	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
>> +	unsigned int val;
>> +
>> +	switch (size) {
>> +	/*
>> +	 * There are two different variants of the AXI AD485X IP block, a 16-
>> bit
>> +	 * and a 20-bit variant.
>> +	 * The 0x0 value (AD485X_PACKET_FORMAT_20BIT) is corresponding also
>> to
>> +	 * the 16-bit variant of the IP block.
>> +	 */
>> +	case 16:
>> +	case 20:
>> +		val = AD485X_PACKET_FORMAT_20BIT;
>> +		break;
>> +	case 24:
>> +		val = AD485X_PACKET_FORMAT_24BIT;
>> +		break;
>> +	/*
>> +	 * The 0x2 (AD485X_PACKET_FORMAT_32BIT) corresponds only to the 20-
>> bit
>> +	 * variant of the IP block. Setting this value properly is ensured by
>> +	 * the upper layers of the drivers calling the axi-adc functions.
>> +	 * Also, for 16-bit IP block, the 0x2 (AD485X_PACKET_FORMAT_32BIT)
>> +	 * value is handled as maximum size available which is 24-bit for
>> this
>> +	 * configuration.
>> +	 */
>> +	case 32:
>> +		val = AD485X_PACKET_FORMAT_32BIT;
>> +		break;
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +
>> +	return regmap_update_bits(st->regmap, ADI_AXI_ADC_REG_CNTRL_3,
>> +				  AD485X_CNTRL_3_PACKET_FORMAT_MSK,
>> +				 
>> FIELD_PREP(AD485X_CNTRL_3_PACKET_FORMAT_MSK, val));
>> +}
>> +
>>  static struct iio_buffer *axi_adc_request_buffer(struct iio_backend *back,
>>  						 struct iio_dev *indio_dev)
>>  {
>> @@ -360,6 +405,7 @@ static const struct iio_backend_ops adi_axi_adc_ops = {
>>  	.test_pattern_set = axi_adc_test_pattern_set,
>>  	.chan_status = axi_adc_chan_status,
>>  	.interface_type_get = axi_adc_interface_type_get,
>> +	.data_size_set = axi_adc_data_size_set,
>>  	.debugfs_reg_access = iio_backend_debugfs_ptr(axi_adc_reg_access),
>>  	.debugfs_print_chan_status =
>> iio_backend_debugfs_ptr(axi_adc_debugfs_print_chan_status),
>>  };
> 
> 

Since these register values are specific to the AD485X variant of the AXI ADC,
I still feel like it would be better if we added a new compatible string like
we did for AD355X on the AXI DAC.

These functions accessing the CNTRL_3 register aren't applicable to the generic
AXI ADC IP block, but only to the AXI AD485X IP core [1]. The AXI AD7606X IP
core [2] that we are working on also uses this same register for other purposes,
so we will have a conflict. We are planning on adding a new AXI ADC compatible
string for AD7606X [3], so I think we should do the same here.

[1]: http://analogdevicesinc.github.io/hdl/library/axi_ad485x/index.html
[2]: http://analogdevicesinc.github.io/hdl/library/axi_ad7606x/index.html
[3]: https://lore.kernel.org/linux-iio/20241210-ad7606_add_iio_backend_software_mode-v2-2-6619c3e50d81@baylibre.com/