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

Martin Blumenstingl martin.blumenstingl at googlemail.com
Tue Oct 31 13:01:43 PDT 2017

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 at googlemail.com>
 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);

More information about the linux-amlogic mailing list