media: i2c: imx477: Disable temperature sensor when enabling XVS

On IMX477 it appears that the on-chip temperature sensor causes
XVS (external sync out) to pulse every ~2ms when not streaming.

So now we do a little dance: Temperature sensor is enabled during
common register setup, giving it time to warm up (almost literally;
otherwise the first frame's reading might be 0C), disabled before
enabling sync out, then enabled again once the camera is streaming.

We already took care to disable XVS output in stop_streaming()
(though previously it wasn't understood why this was needed).

Signed-off-by: Nick Hollinghurst <nick.hollinghurst@raspberrypi.com>

Author: njhollinghurst

drivers/media/i2c/imx477.c

@@ -112,6 +112,9 @@ MODULE_PARM_DESC(trigger_mode, "Set vsync trigger mode: 1=source, 2=sink");
 #define IMX477_REG_XVS_IO_CTRL		0x3040
 #define IMX477_REG_EXTOUT_EN		0x4b81
 
+/* Temperature sensor */
+#define IMX477_REG_TEMP_SEN_CTL		0x0138
+
 /* Embedded metadata stream structure */
 #define IMX477_EMBEDDED_LINE_WIDTH 16384
 #define IMX477_NUM_EMBEDDED_LINES 1
@@ -1833,18 +1836,28 @@ static int imx477_start_streaming(struct imx477 *imx477)
 
 	/* Set vsync trigger mode: 0=standalone, 1=source, 2=sink */
 	tm = (imx477->trigger_mode_of >= 0) ? imx477->trigger_mode_of : trigger_mode;
-	imx477_write_reg(imx477, IMX477_REG_MC_MODE,
-			 IMX477_REG_VALUE_08BIT, (tm > 0) ? 1 : 0);
+	if (tm == 1)
+		imx477_write_reg(imx477, IMX477_REG_TEMP_SEN_CTL,
+				 IMX477_REG_VALUE_08BIT, 0);
+	imx477_write_reg(imx477, IMX477_REG_EXTOUT_EN,
+			IMX477_REG_VALUE_08BIT, (tm == 1) ? 1 : 0);
 	imx477_write_reg(imx477, IMX477_REG_MS_SEL,
 			 IMX477_REG_VALUE_08BIT, (tm <= 1) ? 1 : 0);
 	imx477_write_reg(imx477, IMX477_REG_XVS_IO_CTRL,
 			 IMX477_REG_VALUE_08BIT, (tm == 1) ? 1 : 0);
-	imx477_write_reg(imx477, IMX477_REG_EXTOUT_EN,
-			 IMX477_REG_VALUE_08BIT, (tm == 1) ? 1 : 0);
+	imx477_write_reg(imx477, IMX477_REG_MC_MODE,
+			 IMX477_REG_VALUE_08BIT, (tm > 0) ? 1 : 0);
 
 	/* set stream on register */
-	return imx477_write_reg(imx477, IMX477_REG_MODE_SELECT,
-				IMX477_REG_VALUE_08BIT, IMX477_MODE_STREAMING);
+	ret = imx477_write_reg(imx477, IMX477_REG_MODE_SELECT,
+			       IMX477_REG_VALUE_08BIT, IMX477_MODE_STREAMING);
+
+	/* now it's safe to re-enable temp sensor without glitching XVS */
+	if (tm == 1)
+		imx477_write_reg(imx477, IMX477_REG_TEMP_SEN_CTL,
+				 IMX477_REG_VALUE_08BIT, 1);
+
+	return ret;
 }
 
 /* Stop streaming */