hwmon: do not init sensors on startup

The U-Boot Design Principles[1] clearly say:

  Initialize devices only when they are needed within U-Boot, i.e. don't
  initialize the Ethernet interface(s) unless U-Boot performs a download
  over Ethernet; don't initialize any IDE or USB devices unless U-Boot
  actually tries to load files from these, etc. (and don't forget to
  shut down these devices after using them - otherwise nasty things may
  happen when you try to boot your OS).

So, do not initialize and read the sensors on startup.

Signed-off-by: Heiko Schocher <hs@denx.de>
cc: Wolfgang Denk <wd@denx.de>
cc: Holger Brunck <holger.brunck@keymile.com>

1 files changed, 14 insertions, 2 deletions

diff --git a/common/cmd_dtt.c b/common/cmd_dtt.c
index 3388e43ca0..5bba12d4d0 100644
--- a/common/cmd_dtt.c
+++ b/common/cmd_dtt.c
@@ -28,12 +28,16 @@
 #include <dtt.h>
 #include <i2c.h>
 
+static unsigned long sensor_initialized;
+
 int do_dtt (cmd_tbl_t * cmdtp, int flag, int argc, char * const argv[])
 {
 	int i;
 	unsigned char sensors[] = CONFIG_DTT_SENSORS;
 	int old_bus;
 
+	/* Force a compilation error, if there are more then 32 sensors */
+	BUILD_BUG_ON(sizeof(sensors) > 32);
 	/* switch to correct I2C bus */
 	old_bus = I2C_GET_BUS();
 	I2C_SET_BUS(CONFIG_SYS_DTT_BUS_NUM);
@@ -42,8 +46,16 @@ int do_dtt (cmd_tbl_t * cmdtp, int flag, int argc, char * const argv[])
 	 * Loop through sensors, read
 	 * temperature, and output it.
 	 */
-	for (i = 0; i < sizeof (sensors); i++)
-		printf ("DTT%d: %i C\n", i + 1, dtt_get_temp (sensors[i]));
+	for (i = 0; i < sizeof(sensors); i++) {
+		if ((sensor_initialized & (1 << i)) == 0) {
+			if (dtt_init_one(sensors[i]) != 0) {
+				printf("DTT%d: Failed init!\n", i);
+				continue;
+			}
+			sensor_initialized |= (1 << i);
+		}
+		printf("DTT%d: %i C\n", i + 1, dtt_get_temp(sensors[i]));
+	}
 
 	/* switch back to original I2C bus */
 	I2C_SET_BUS(old_bus);