[PATCH 3/5] iio: at91: ADC start-up time calculation changed since at91sam9x5

[Josh Wu]

Since in at91sam9x5, sama5d3x chip. the start up time calucation is changed.
And these two chips also have TSMR, so we check whether ADC has TSMR, then
choose different start up time calculation formula.

Signed-off-by: Josh Wu <josh.wu at atmel.com>
---
 drivers/iio/adc/at91_adc.c |   40 +++++++++++++++++++++++++++++++++-------
 1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/adc/at91_adc.c b/drivers/iio/adc/at91_adc.c
index 14e99ba..e93a075 100644
--- a/drivers/iio/adc/at91_adc.c
+++ b/drivers/iio/adc/at91_adc.c
@@ -733,13 +733,39 @@ static int at91_adc_probe(struct platform_device *pdev)
 		goto error_disable_adc_clk;
 	}
 
-	/*
-	 * Number of ticks needed to cover the startup time of the ADC as
-	 * defined in the electrical characteristics of the board, divided by 8.
-	 * The formula thus is : Startup Time = (ticks + 1) * 8 / ADC Clock
-	 */
-	ticks = round_up((st->startup_time * adc_clk_khz /
-			  1000) - 1, 8) / 8;
+	if (!st->caps.has_tsmr) {
+		/*
+		 * Number of ticks needed to cover the startup time of the ADC
+		 * as defined in the electrical characteristics of the board,
+		 * divided by 8. The formula thus is :
+		 *   Startup Time = (ticks + 1) * 8 / ADC Clock
+		 */
+		ticks = round_up((st->startup_time * adc_clk_khz /
+				  1000) - 1, 8) / 8;
+	} else {
+		/*
+		 * For sama5d3x and at91sam9x5, the formula changes to:
+		 * Startup Time = <lookup_table_value> / ADC Clock
+		 */
+		const int startup_lookup[] = {
+			0  , 8  , 16 , 24 ,
+			64 , 80 , 96 , 112,
+			512, 576, 640, 704,
+			768, 832, 896, 960
+			};
+
+		int i, size = ARRAY_SIZE(startup_lookup);
+		ticks = st->startup_time * adc_clk_khz / 1000;
+		for (i = 0; i < size; i++)
+			if (ticks < startup_lookup[i])
+				break;
+
+		ticks = i;
+		if (ticks == size)
+			/* Reach the end of lookup table */
+			ticks = size - 1;
+	}
+
 	/*
 	 * a minimal Sample and Hold Time is necessary for the ADC to guarantee
 	 * the best converted final value between two channels selection
-- 
1.7.10