Re: [PATCH 1/5] iio: adc: meson-saradc: fix the bit_idx of the adc_en clock

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 31 Oct 2017 21:01:43 +0100
Martin Blumenstingl <martin.blumenstingl@googlemail.com> wrote:

> Meson8 and Meson8b SoCs use the the SAR ADC gate clock provided by the
> MESON_SAR_ADC_REG3 register within the SAR ADC register area.
> According to the datasheet (and the existing MESON_SAR_ADC_REG3_CLK_EN
> definition) the gate is on bit 30.
> The fls() function returns the last set bit, which is "bit index + 1"
> (fls(MESON_SAR_ADC_REG3_CLK_EN) returns 31). Fix this by switching to
> __ffs() which returns the first set bit, which is bit 30 in our case.
> 
> This off by one error results in the ADC not being usable on devices
> where the bootloader did not enable the clock.
> 
> Fixes: 3adbf3427330 ("iio: adc: add a driver for the SAR ADC found in Amlogic Meson SoCs")
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Applied to the fixes-togreg branch of iio.git and marked for stable.

Thanks,

Jonathan
> ---
>  drivers/iio/adc/meson_saradc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/meson_saradc.c b/drivers/iio/adc/meson_saradc.c
> index 2e8dbb89c8c9..55611244c799 100644
> --- a/drivers/iio/adc/meson_saradc.c
> +++ b/drivers/iio/adc/meson_saradc.c
> @@ -600,7 +600,7 @@ static int meson_sar_adc_clk_init(struct iio_dev *indio_dev,
>  	init.num_parents = 1;
>  
>  	priv->clk_gate.reg = base + MESON_SAR_ADC_REG3;
> -	priv->clk_gate.bit_idx = fls(MESON_SAR_ADC_REG3_CLK_EN);
> +	priv->clk_gate.bit_idx = __ffs(MESON_SAR_ADC_REG3_CLK_EN);
>  	priv->clk_gate.hw.init = &init;
>  
>  	priv->adc_clk = devm_clk_register(&indio_dev->dev, &priv->clk_gate.hw);