media: ov7670: don't access registers when the device is powered off

Since commit 3d6a8fe2 ("media: ov7670: hook s_power onto v4l2 core"),
the device is actually powered off while the video stream is stopped.

So now set_format and s_frame_interval could be called while the device
is powered off, but these callbacks try to change the register settings
at this time.

The frame format and framerate will be restored right after power-up, so
we can just postpone applying these changes at these callbacks if the
device is not powered up.

Fixes: 3d6a8fe2 ("media: ov7670: hook s_power onto v4l2 core")

Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Reviewed-by: Lubomir Rintel <lkundrak@v3.sk>
Tested-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/i2c/ov7670.c

@@ -864,7 +864,15 @@ static int ov7675_set_framerate(struct v4l2_subdev *sd,
 	/* Recalculate frame rate */
 	ov7675_get_framerate(sd, tpf);
 
-	return ov7675_apply_framerate(sd);
+	/*
+	 * If the device is not powered up by the host driver do
+	 * not apply any changes to H/W at this time. Instead
+	 * the framerate will be restored right after power-up.
+	 */
+	if (info->on)
+		return ov7675_apply_framerate(sd);
+
+	return 0;
 }
 
 static void ov7670_get_framerate_legacy(struct v4l2_subdev *sd,
@@ -895,7 +903,16 @@ static int ov7670_set_framerate_legacy(struct v4l2_subdev *sd,
 	info->clkrc = (info->clkrc & 0x80) | div;
 	tpf->numerator = 1;
 	tpf->denominator = info->clock_speed / div;
-	return ov7670_write(sd, REG_CLKRC, info->clkrc);
+
+	/*
+	 * If the device is not powered up by the host driver do
+	 * not apply any changes to H/W at this time. Instead
+	 * the framerate will be restored right after power-up.
+	 */
+	if (info->on)
+		return ov7670_write(sd, REG_CLKRC, info->clkrc);
+
+	return 0;
 }
 
 /*
@@ -1105,9 +1122,13 @@ static int ov7670_set_fmt(struct v4l2_subdev *sd,
 	if (ret)
 		return ret;
 
-	ret = ov7670_apply_fmt(sd);
-	if (ret)
-		return ret;
+	/*
+	 * If the device is not powered up by the host driver do
+	 * not apply any changes to H/W at this time. Instead
+	 * the frame format will be restored right after power-up.
+	 */
+	if (info->on)
+		return ov7670_apply_fmt(sd);
 
 	return 0;
 }