Re: [PATCH v4 05/15] iio: adc: xilinx-xadc: Use bitfield helpers and bit macros

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 5 Oct 2026 15:11:55 +0530
Dileep Kumar Nagavarapu <dileepkumar.nagavarapu@amd.com> wrote:

> Replace open-coded bit manipulation with FIELD_GET(),
> FIELD_PREP(), BIT(), and GENMASK() helpers.
> 
> Using the kernel bitfield helpers improves readability and
> makes bit operations less error-prone.
> 
> No functional changes intended.
> 
> Co-developed-by: Sai Krishna Potthuri <sai.krishna.potthuri@amd.com>
> Signed-off-by: Sai Krishna Potthuri <sai.krishna.potthuri@amd.com>
> Signed-off-by: Dileep Kumar Nagavarapu <dileepkumar.nagavarapu@amd.com>
> ---
>  drivers/iio/adc/xilinx-xadc-core.c | 25 +++++++++++++------------
>  drivers/iio/adc/xilinx-xadc.h      | 24 ++++++++++++------------
>  2 files changed, 25 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
> index b4a3e6f967c4..9e4955016bbc 100644
> --- a/drivers/iio/adc/xilinx-xadc-core.c
> +++ b/drivers/iio/adc/xilinx-xadc-core.c
> @@ -11,6 +11,8 @@
>   *  - AXI XADC interface: Xilinx PG019
>   */
>  
> +#include <linux/bitfield.h>
> +#include <linux/bits.h>
>  #include <linux/clk.h>
>  #include <linux/device.h>
>  #include <linux/err.h>
> @@ -47,18 +49,17 @@ static const unsigned int XADC_ZYNQ_UNMASK_TIMEOUT = 500;
>  #define XADC_ZYNQ_REG_CTL		0x18
>  
>  #define XADC_ZYNQ_CFG_ENABLE		BIT(31)
> -#define XADC_ZYNQ_CFG_DFIFOTH_MASK	(0xf << 16)
> -#define XADC_ZYNQ_CFG_DFIFOTH_OFFSET	16
>  #define XADC_ZYNQ_CFG_REDGE		BIT(12)
> -#define XADC_ZYNQ_CFG_TCKRATE_MASK	(0x3 << 8)
> -#define XADC_ZYNQ_CFG_TCKRATE_DIV2	(0x0 << 8)
> -#define XADC_ZYNQ_CFG_TCKRATE_DIV4	(0x1 << 8)
> -#define XADC_ZYNQ_CFG_TCKRATE_DIV8	(0x2 << 8)
> -#define XADC_ZYNQ_CFG_TCKRATE_DIV16	(0x3 << 8)
> +#define XADC_ZYNQ_CFG_DFIFOTH_MASK	GENMASK(19, 16)
> +#define XADC_ZYNQ_CFG_TCKRATE_MASK	GENMASK(9, 8)
> +#define XADC_ZYNQ_CFG_TCKRATE_DIV2	0
> +#define XADC_ZYNQ_CFG_TCKRATE_DIV4	BIT(8)
> +#define XADC_ZYNQ_CFG_TCKRATE_DIV8	BIT(9)
> +#define XADC_ZYNQ_CFG_TCKRATE_DIV16	GENMASK(9, 8)

These are the values 0, 1, 2 and 3 in the field TCKRATE
so why would we define them as bit masks.  Just use the
numbers.

>  #define XADC_ZYNQ_CFG_IGAP(x)		(x)
>  
>  #define XADC_ZYNQ_INT_DFIFO_GTH		BIT(8)
> -#define XADC_ZYNQ_INT_ALARM_MASK	0xff
> +#define XADC_ZYNQ_INT_ALARM_MASK	GENMASK(7, 0)
>  
>  #define XADC_ZYNQ_STATUS_DFIFOE		BIT(8)
>  
> @@ -86,7 +87,7 @@ static const unsigned int XADC_ZYNQ_UNMASK_TIMEOUT = 500;
>  #define XADC_AXI_GIER_ENABLE		BIT(31)
>  
>  #define XADC_AXI_INT_EOS		BIT(4)
> -#define XADC_AXI_INT_ALARM_MASK		0x3c0f
> +#define XADC_AXI_INT_ALARM_MASK		(GENMASK(13, 10) | GENMASK(3, 0))

That's an odd mask. Is it made up of fields you can break it down into?


>  
>  static int xadc_write_raw(struct iio_dev *indio_dev,
> diff --git a/drivers/iio/adc/xilinx-xadc.h b/drivers/iio/adc/xilinx-xadc.h
> index 8449fb741370..a659b7981b2f 100644
> --- a/drivers/iio/adc/xilinx-xadc.h
> +++ b/drivers/iio/adc/xilinx-xadc.h
> @@ -9,6 +9,7 @@
>  #ifndef __IIO_XILINX_XADC__
>  #define __IIO_XILINX_XADC__
>  
> +#include <linux/bits.h>
>  #include <linux/interrupt.h>
>  #include <linux/mutex.h>
>  #include <linux/spinlock.h>
> @@ -141,20 +142,19 @@ static inline int xadc_write_adc_reg(struct xadc *xadc, unsigned int reg, u16 va
>  #define XADC_CONF0_MUX			BIT(11)
>  #define XADC_CONF0_CHAN(x)		(x)
>  
> -#define XADC_CONF1_SEQ_MASK		(0xf << 12)
> -#define XADC_CONF1_SEQ_DEFAULT		(0 << 12)
> -#define XADC_CONF1_SEQ_CONTINUOUS	(2 << 12)
> -#define XADC_CONF1_SEQ_SIMULTANEOUS	(4 << 12)
> -#define XADC_CONF1_SEQ_INDEPENDENT	(8 << 12)
> -#define XADC_CONF1_ALARM_MASK		0x0f0f
> +#define XADC_CONF1_SEQ_MASK		GENMASK(15, 12)
Interesting corner case. How is it documented?
Are the bits a bitmap or is it a larger field where only
the values 0, 2, 4 and 8 are not reserved?

Hopefully it isn't that most horrible of datasheet things
a bitmap inside a field.  Those are hard to write nice
software for because you end up with a FIELD_PREP(BIT() like
you have here.

> +#define XADC_CONF1_SEQ_DEFAULT		0
> +#define XADC_CONF1_SEQ_CONTINUOUS	BIT(13)
> +#define XADC_CONF1_SEQ_SIMULTANEOUS	BIT(14)
> +#define XADC_CONF1_SEQ_INDEPENDENT	BIT(15)
> +#define XADC_CONF1_ALARM_MASK		(GENMASK(11, 8) | GENMASK(3, 0))

Similar to above. I'm hoping that can be broken down into more
specific fields. Otherwise we are magic number territory rather
than a normal bitmask for a field.

>  
> -#define XADC_CONF2_DIV_MASK	0xff00
> -#define XADC_CONF2_DIV_OFFSET	8
> +#define XADC_CONF2_DIV_MASK	GENMASK(15, 8)
>  
> -#define XADC_CONF2_PD_MASK	(0x3 << 4)
> -#define XADC_CONF2_PD_NONE	(0x0 << 4)
> -#define XADC_CONF2_PD_ADC_B	(0x2 << 4)
> -#define XADC_CONF2_PD_BOTH	(0x3 << 4)
> +#define XADC_CONF2_PD_MASK	GENMASK(5, 4)
> +#define XADC_CONF2_PD_NONE	0
> +#define XADC_CONF2_PD_ADC_B	BIT(5)
Smells like a value of 2
> +#define XADC_CONF2_PD_BOTH	GENMASK(5, 4)
and a value of 3 - so keep it as those.

>  
>  #define XADC_ALARM_VCCINT_MASK		BIT(1)
>  #define XADC_ALARM_VCCAUX_MASK		BIT(2)