Re: [PATCH 4/5] iio: adc: meson-saradc: fix the clock frequency on Meson8 and Meson8b

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 31 Oct 2017 21:01:46 +0100
Martin Blumenstingl <martin.blumenstingl@googlemail.com> wrote:

> GX SoCs use a 1.2 MHz ADC clock, while the older SoCs use a 1.14 MHz
> clock.
> 
> A comment in the driver from Amlogic's GPL kernel says that it's
> running at 1.28 MHz. However, it's actually programming a divider of
> 20 + 1. With a XTAL clock of 24 MHz this results in a frequency of
> 1.14 MHz. (their calculation might be based on a 27 MHz XTAL clock,
> but this is not what we have on the Meson8 and Meson8b SoCs).
> 
> The ADC was still working with the 1.2MHz clock. In my own tests I did
> not see a difference between 1.2 and 1.14 MHz (regardless of the clock
> frequency used, the ADC results were identical).
> 
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

Hmm. This will have to wait until the other patches have gotten into
mainline and back to my upstream.  Let me know if I seem to have lost
it. 

Thanks,

 
Jonathan

> ---
>  drivers/iio/adc/meson_saradc.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
> index 7dc7d297a0fc..fa3c1378c2c9 100644
> --- a/drivers/iio/adc/meson_saradc.c
> +++ b/drivers/iio/adc/meson_saradc.c
> @@ -221,6 +221,7 @@ enum meson_sar_adc_chan7_mux_sel {
>  
>  struct meson_sar_adc_data {
>  	bool					has_bl30_integration;
> +	unsigned long				clock_rate;
>  	u32					bandgap_reg;
>  	unsigned int				resolution;
>  	const char				*name;
> @@ -684,7 +685,7 @@ static int meson_sar_adc_init(struct iio_dev *indio_dev)
>  		return ret;
>  	}
>  
> -	ret = clk_set_rate(priv->adc_clk, 1200000);
> +	ret = clk_set_rate(priv->adc_clk, priv->data->clock_rate);
>  	if (ret) {
>  		dev_err(indio_dev->dev.parent,
>  			"failed to set adc clock rate\n");
> @@ -867,6 +868,7 @@ static const struct iio_info meson_sar_adc_iio_info = {
>  
>  static const struct meson_sar_adc_data meson_sar_adc_meson8_data = {
>  	.has_bl30_integration = false,
> +	.clock_rate = 1150000,
>  	.bandgap_reg = MESON_SAR_ADC_DELTA_10,
>  	.regmap_config = &meson_sar_adc_regmap_config_meson8,
>  	.resolution = 10,
> @@ -875,6 +877,7 @@ static const struct meson_sar_adc_data meson_sar_adc_meson8_data = {
>  
>  static const struct meson_sar_adc_data meson_sar_adc_meson8b_data = {
>  	.has_bl30_integration = false,
> +	.clock_rate = 1150000,
>  	.bandgap_reg = MESON_SAR_ADC_DELTA_10,
>  	.regmap_config = &meson_sar_adc_regmap_config_meson8,
>  	.resolution = 10,
> @@ -883,6 +886,7 @@ static const struct meson_sar_adc_data meson_sar_adc_meson8b_data = {
>  
>  static const struct meson_sar_adc_data meson_sar_adc_gxbb_data = {
>  	.has_bl30_integration = true,
> +	.clock_rate = 1200000,
>  	.bandgap_reg = MESON_SAR_ADC_REG11,
>  	.regmap_config = &meson_sar_adc_regmap_config_gxbb,
>  	.resolution = 10,
> @@ -891,6 +895,7 @@ static const struct meson_sar_adc_data meson_sar_adc_gxbb_data = {
>  
>  static const struct meson_sar_adc_data meson_sar_adc_gxl_data = {
>  	.has_bl30_integration = true,
> +	.clock_rate = 1200000,
>  	.bandgap_reg = MESON_SAR_ADC_REG11,
>  	.regmap_config = &meson_sar_adc_regmap_config_gxbb,
>  	.resolution = 12,
> @@ -899,6 +904,7 @@ static const struct meson_sar_adc_data meson_sar_adc_gxl_data = {
>  
>  static const struct meson_sar_adc_data meson_sar_adc_gxm_data = {
>  	.has_bl30_integration = true,
> +	.clock_rate = 1200000,
>  	.bandgap_reg = MESON_SAR_ADC_REG11,
>  	.regmap_config = &meson_sar_adc_regmap_config_gxbb,
>  	.resolution = 12,