linux-kernel - Re: [PATCH v3 4/7] iio: imu: adis16480: Calculate the sampling frequency in a generic way

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Date:   Sun, 3 Mar 2019 12:51:03 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Stefan Popa <stefan.popa@...log.com>
Cc:     <robh+dt@...nel.org>, <Michael.Hennerich@...log.com>,
        <knaack.h@....de>, <lars@...afoo.de>, <pmeerw@...erw.net>,
        <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
        <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 4/7] iio: imu: adis16480: Calculate the sampling
 frequency in a generic way

On Wed, 27 Feb 2019 18:14:25 +0200
Stefan Popa <stefan.popa@...log.com> wrote:

> The adis1648x devices have an internal clock of 2.46 kSPS. The sampling
> frequency is calculated by applying a decimation rate which can take the
> maximum value of 2047.
> 
> Although all adis1648x devices are similar in this regard, devices that
> will use this feature will be added in the future.
> 
> Signed-off-by: Stefan Popa <stefan.popa@...log.com>
Straight forward refactor so fine.

Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

A comment inline about something in the old code!

Thanks,

Jonathan

> ---
>  drivers/iio/imu/adis16480.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/imu/adis16480.c b/drivers/iio/imu/adis16480.c
> index 5a2864a..92abc95 100644
> --- a/drivers/iio/imu/adis16480.c
> +++ b/drivers/iio/imu/adis16480.c
> @@ -125,6 +125,8 @@ struct adis16480_chip_info {
>  	unsigned int accel_max_val;
>  	unsigned int accel_max_scale;
>  	unsigned int temp_scale;
> +	unsigned int int_clk;
> +	unsigned int max_dec_rate;
>  };
>  
>  enum adis16480_int_pin {
> @@ -299,9 +301,9 @@ static int adis16480_set_freq(struct iio_dev *indio_dev, int val, int val2)
>  	if (t <= 0)
>  		return -EINVAL;
>  
> -	t = 2460000 / t;
> -	if (t > 2048)
> -		t = 2048;
> +	t = st->chip_info->int_clk / t;
> +	if (t > st->chip_info->max_dec_rate)
> +		t = st->chip_info->max_dec_rate;
>  
>  	if (t != 0)
>  		t--;
> @@ -320,7 +322,7 @@ static int adis16480_get_freq(struct iio_dev *indio_dev, int *val, int *val2)
>  	if (ret < 0)
>  		return ret;
>  
> -	freq = 2460000 / (t + 1);
> +	freq = st->chip_info->int_clk / (t + 1);

I'm a little curious about why t + 1?  Presumably to avoid weird rounding
issues, but maybe a nice addition would be a comment explaining this.

>  	*val = freq / 1000;
>  	*val2 = (freq % 1000) * 1000;
>  
> @@ -726,6 +728,8 @@ static const struct adis16480_chip_info adis16480_chip_info[] = {
>  		.accel_max_val = IIO_M_S_2_TO_G(21973),
>  		.accel_max_scale = 18,
>  		.temp_scale = 5650, /* 5.65 milli degree Celsius */
> +		.int_clk = 2460000,
> +		.max_dec_rate = 2048,
>  	},
>  	[ADIS16480] = {
>  		.channels = adis16480_channels,
> @@ -735,6 +739,8 @@ static const struct adis16480_chip_info adis16480_chip_info[] = {
>  		.accel_max_val = IIO_M_S_2_TO_G(12500),
>  		.accel_max_scale = 10,
>  		.temp_scale = 5650, /* 5.65 milli degree Celsius */
> +		.int_clk = 2460000,
> +		.max_dec_rate = 2048,
>  	},
>  	[ADIS16485] = {
>  		.channels = adis16485_channels,
> @@ -744,6 +750,8 @@ static const struct adis16480_chip_info adis16480_chip_info[] = {
>  		.accel_max_val = IIO_M_S_2_TO_G(20000),
>  		.accel_max_scale = 5,
>  		.temp_scale = 5650, /* 5.65 milli degree Celsius */
> +		.int_clk = 2460000,
> +		.max_dec_rate = 2048,
>  	},
>  	[ADIS16488] = {
>  		.channels = adis16480_channels,
> @@ -753,6 +761,8 @@ static const struct adis16480_chip_info adis16480_chip_info[] = {
>  		.accel_max_val = IIO_M_S_2_TO_G(22500),
>  		.accel_max_scale = 18,
>  		.temp_scale = 5650, /* 5.65 milli degree Celsius */
> +		.int_clk = 2460000,
> +		.max_dec_rate = 2048,
>  	},
>  };
>