Hi Dongchun,

On Tue, Mar 10, 2020 at 06:00:19PM +0800, Dongchun Zhu wrote:

Hi Sakari, Rob, Andy, Tomasz,

On Fri, 2020-02-28 at 23:59 +0800, Dongchun Zhu wrote:

...

quoted

+static int dw9768_init(struct dw9768 *dw9768)
+{
+	struct i2c_client *client = v4l2_get_subdevdata(&dw9768->sd);
+	int ret, val;
+
+	/* Reset DW9768_RING_PD_CONTROL_REG to default status 0x00 */
+	ret = i2c_smbus_write_byte_data(client, DW9768_RING_PD_CONTROL_REG,
+					DW9768_PD_MODE_OFF);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * DW9769 requires waiting delay time of t_OPR
+	 * after PD reset takes place.
+	 */
+	usleep_range(DW9768_T_OPR_US, DW9768_T_OPR_US + 100);
+
+	ret = dw9768_write_array(dw9768, dw9768_init_regs,
+				 ARRAY_SIZE(dw9768_init_regs));
+	if (ret)
+		return ret;
+
+	for (val = dw9768->focus->val % DW9768_MOVE_STEPS;
+	     val <= dw9768->focus->val;
+	     val += DW9768_MOVE_STEPS) {
+		ret = dw9768_set_dac(dw9768, val);
+		if (ret) {
+			dev_err(&client->dev, "%s I2C failure: %d",
+				__func__, ret);
+			return ret;
+		}
+		usleep_range(DW9768_MOVE_DELAY_US,
+			     DW9768_MOVE_DELAY_US + 1000);
+	}
+

What do you think about the approach taken by this patch?
From the view of VCM hardware, the collision sound of lens should only
happen when moving position back to zero.
When opening camera, one should be able to move lens to the position
directly.
I tried to replace this code to a single dw9768_set_dac(dw9768,
dw9768->focus->val),
there is no collision sound when open camera and it could reduce several
hundred ms when open lens driver fd.
Are we okay with this?

I think so. Usually on VCMs with ringing compensation the only problematic
case is when the power is cut. :-)

-- 
Sakari Ailus

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