[U-Boot,RFT,2/8] exynos: Wait till ADC stabilizes before checking Odroid HC1 revision

Message ID 20190209225411.32756-3-krzk@kernel.org
State RFC
Delegated to: Minkyu Kang
Headers show
Series
  • exynos: Fix reboot on Odroid HC1
Related show

Commit Message

Krzysztof Kozlowski Feb. 9, 2019, 10:54 p.m.
Fix detection of Odroid HC1 (Exynos5422) after reboot if kernel disabled
the LDO4/VDD_ADC regulator.

The LDO4 supplies both ADC block and the ADC input AIN9.  Voltage on
AIN9 will rise slowly, so be patient and wait for it to stabilize.

First reads on Odroid HC1 return 305, 1207, 1297 and finally 1308
(reference value is 1309).

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
---
 board/samsung/common/exynos5-dt-types.c | 34 ++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

Patch

diff --git a/board/samsung/common/exynos5-dt-types.c b/board/samsung/common/exynos5-dt-types.c
index 7a86e9187768..ba8584f1a5d8 100644
--- a/board/samsung/common/exynos5-dt-types.c
+++ b/board/samsung/common/exynos5-dt-types.c
@@ -57,12 +57,44 @@  static unsigned int odroid_get_rev(void)
 	return 0;
 }
 
+/*
+ * Read ADC at least twice and check the resuls.  If regulator providing voltage
+ * on to measured point was just turned on, first reads might require time
+ * to stabilize.
+ */
+static int odroid_get_adc_val(unsigned int *adcval)
+{
+	unsigned int adcval_prev = 0;
+	int ret, retries = 20;
+
+	ret = adc_channel_single_shot("adc", CONFIG_ODROID_REV_AIN,
+				      &adcval_prev);
+	if (ret)
+		return ret;
+
+	while (retries--) {
+		mdelay(5);
+
+		ret = adc_channel_single_shot("adc", CONFIG_ODROID_REV_AIN,
+					      adcval);
+		if (ret)
+			return ret;
+
+		if ((100 * abs(*adcval - adcval_prev) / adcval_prev) < 3)
+			return ret;
+
+		adcval_prev = *adcval;
+	}
+
+	return ret;
+}
+
 static int odroid_get_board_type(void)
 {
 	unsigned int adcval;
 	int ret, i;
 
-	ret = adc_channel_single_shot("adc", CONFIG_ODROID_REV_AIN, &adcval);
+	ret = odroid_get_adc_val(&adcval);
 	if (ret)
 		goto rev_default;