ENGR00327364 iMX6x: Ensure that the bandgap self-bias circuit is disabled after boot.rel_imx_3.0.101_4.1.1imx_v2009.08_3.0.35_4.1.0

The self-bias circuit is used by the bandgap during startup.
Once the bandgap has stabilized, the self-bias circuit should be
disabled for best noise performance of analog blocks.
Also this bit should be disabled before the chip enters STOP mode or
when ever the regular bandgap is disabled.

Backport from imx_v20014.04:fd572f16430d383a6c237f9fe9e96546c957a042

Signed-off-by: Ranjani Vaidyanathan <Ranjani.Vaidyanathan@freescale.com>

1 files changed, 24 insertions, 5 deletions

diff --git a/cpu/arm_cortexa8/mx6/generic.c b/cpu/arm_cortexa8/mx6/generic.c
index ac7fa6e..789db98 100644
--- a/cpu/arm_cortexa8/mx6/generic.c
+++ b/cpu/arm_cortexa8/mx6/generic.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2010-2013 Freescale Semiconductor, Inc.
+ * Copyright (C) 2010-2014 Freescale Semiconductor, Inc.
  *
  * See file CREDITS for list of people who contributed to this
  * project.
@@ -916,8 +916,6 @@ static inline int read_cpu_temperature(void)
 	the temperature, we will power on/down the anadig module*/
 	writel(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
 			ANATOP_BASE_ADDR + HW_ANADIG_TEMPSENSE0_CLR);
-	writel(BM_ANADIG_ANA_MISC0_REFTOP_SELBIASOFF,
-			ANATOP_BASE_ADDR + HW_ANADIG_ANA_MISC0_SET);
 
 	/* write measure freq */
 	reg = readl(ANATOP_BASE_ADDR + HW_ANADIG_TEMPSENSE1);
@@ -953,8 +951,6 @@ static inline int read_cpu_temperature(void)
 	/* power down anatop thermal sensor */
 	writel(BM_ANADIG_TEMPSENSE0_POWER_DOWN,
 			ANATOP_BASE_ADDR + HW_ANADIG_TEMPSENSE0_SET);
-	writel(BM_ANADIG_ANA_MISC0_REFTOP_SELBIASOFF,
-			ANATOP_BASE_ADDR + HW_ANADIG_ANA_MISC0_CLR);
 
 	return temperature;
 
@@ -1031,6 +1027,22 @@ int cpu_eth_init(bd_t *bis)
 	return rc;
 }
 
+static void init_bandgap(void)
+{
+	/*
+	* Ensure the bandgap has stabilized.
+	*/
+	while (!(readl(ANATOP_BASE_ADDR + HW_ANADIG_ANA_MISC0) & 0x80))
+		;
+	/*
+	 * For best noise performance of the analog blocks using the
+	 * outputs of the bandgap, the reftop_selfbias_off bit should
+	 * be set.
+	 */
+	writel(BM_ANADIG_ANA_MISC0_REFTOP_SELBIASOFF,
+				ANATOP_BASE_ADDR + HW_ANADIG_ANA_MISC0_SET);
+}
+
 #if defined(CONFIG_ARCH_CPU_INIT)
 int arch_cpu_init(void)
 {
@@ -1039,6 +1051,13 @@ int arch_cpu_init(void)
 	/* Clear MMDC channel mask */
 	writel(0, CCM_BASE_ADDR + 0x4);
 
+	/*
+	 * Disable self-bias circuit in the analog bandap.
+	 * The self-bias circuit is used by the bandgap during startup.
+	 * This bit should be set after the bandgap has initialized.
+	 */
+	init_bandgap();
+
 	/* Due to hardware limitation, on MX6Q we need to gate/ungate all PFDs
 	 * to make sure PFD is working right, otherwise, PFDs may
 	 * not output clock after reset, MX6DL and MX6SL have added 396M pfd