linux-kernel - [PATCH 4.14 024/164] iio: adc: meson-saradc: fix the bit_idx of the adc

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Message-Id: <20171212123445.044398119@linuxfoundation.org>
Date:   Tue, 12 Dec 2017 13:43:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: [PATCH 4.14 024/164] iio: adc: meson-saradc: fix the bit_idx of the adc_en clock

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>

commit 7a6b0420d2fe4ce59437bd318826fe468f0d71ae upstream.

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@...glemail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/iio/adc/meson_saradc.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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
 	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);