linux-kernel - [PATCH] iio: adc: at91_adc: correct default shtim value

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Date:	Mon,  3 Mar 2014 19:07:04 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Josh Wu <josh.wu@...el.com>,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Subject: [PATCH] iio: adc: at91_adc: correct default shtim value

When sample_hold_time is zero (this is the case when DT is not used or if
atmel,adc-sample-hold-time is omitted), then the calculated shtim is large.

Make that 0, which is the default for that register and the ADC will then use a
sane value of 2/ADCCLK or 1/ADCCLK depending on the version.

Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
---
 drivers/iio/adc/at91_adc.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
index 5b1aa027c034..0b103f905607 100644
--- a/drivers/iio/adc/at91_adc.c
+++ b/drivers/iio/adc/at91_adc.c
@@ -1004,8 +1004,11 @@ static int at91_adc_probe(struct platform_device *pdev)
 	 * the best converted final value between two channels selection
 	 * The formula thus is : Sample and Hold Time = (shtim + 1) / ADCClock
 	 */
-	shtim = round_up((st->sample_hold_time * adc_clk_khz /
-			  1000) - 1, 1);
+	if (st->sample_hold_time > 0)
+		shtim = round_up((st->sample_hold_time * adc_clk_khz / 1000)
+				 - 1, 1);
+	else
+		shtim = 0;
 
 	reg = AT91_ADC_PRESCAL_(prsc) & st->registers->mr_prescal_mask;
 	reg |= AT91_ADC_STARTUP_(ticks) & st->registers->mr_startup_mask;
-- 
1.8.3.2

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