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From: "Yeh, Andy" <andy.yeh@intel.com>
To: Sakari Ailus <sakari.ailus@linux.intel.com>,
        "Chen, Ping-chung" <ping-chung.chen@intel.com>
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        "Mani, Rajmohan" <rajmohan.mani@intel.com>
Subject: RE: [PATCH v5] media: imx208: Add imx208 camera sensor driver
Date: Wed, 26 Sep 2018 15:19:16 +0000
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Hi Sakari, PC,

>-----Original Message-----
>From: Sakari Ailus [mailto:sakari.ailus@linux.intel.com]
>Sent: Wednesday, September 26, 2018 6:12 PM
>To: Chen, Ping-chung <ping-chung.chen@intel.com>
>Cc: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>; Laurent Pinchart
><laurent.pinchart@ideasonboard.com>; Sakari Ailus <sakari.ailus@iki.fi>;
>tfiga@chromium.org; sylwester.nawrocki@gmail.com; linux-media <linux-
>media@vger.kernel.org>; Yeh, Andy <andy.yeh@intel.com>; Lai, Jim
><jim.lai@intel.com>; grundler@chromium.org; Mani, Rajmohan
><rajmohan.mani@intel.com>
>Subject: Re: [PATCH v5] media: imx208: Add imx208 camera sensor driver
>
>Hi Ping-chung,
>
>On Wed, Sep 26, 2018 at 02:27:01AM +0000, Chen, Ping-chung wrote:
>> Hi Sakari,
>>
>> >-----Original Message-----
>> >From: Sakari Ailus [mailto:sakari.ailus@linux.intel.com]
>> >Sent: Wednesday, September 26, 2018 5:55 AM
>>
>> >Hi Ping-chung,
>>
>> >On Tue, Sep 25, 2018 at 10:17:48AM +0000, Chen, Ping-chung wrote:
>> >...
>> > > > > Controls that have a documented unit use that unit --- as long
>> > > > > as that's the unit used by the hardware. If it's not, it tends
>> > > > > to be that another unit is used but the user space has
>> > > > > currently no way of knowing this. And the digital gain control is no
>exception to this.
>> > > > >
>> > > > > So if we want to improve the user space's ability to be
>> > > > > informed how the control values reflect to device
>> > > > > configuration, we do need to provide more information to the
>> > > > > user space. One way to do that would be through
>> > > > > VIDIOC_QUERY_EXT_CTRL. The IOCTL struct has plenty of reserved
>fields --- just for purposes such as this one.
>> > > >
>> > > > I don't think we can come up with a good way to expose arbitrary
>> > > > mathematical formulas through an ioctl. In my opinion the
>> > > > question is how far we want to go, how precise we need to be.
>> > > >
>> > > > > > Any opinions or better ideas?
>> > >
>> > > >My 0.02 DKK.  On a similar situation, where userspace was running a
>close loop calibration:
>> > >
>> > > >We have implemented two extra control: eposure_next exposure_pre
>that tell us which one is the next value. Perhaps we could embebed such
>functionality in QUERY_EXT_CTRL.
>> > >
>> > > >Cheers
>> > >
>> > > How about creating an additional control to handle the case of
>> > > V4L2_CID_GAIN in the imx208 driver? HAL can set AG and DG
>> > > separately for the general sensor usage by V4L2_CID_ANALOGUE_GAIN
>> > > and V4L2_CID_DIGITAL_GAIN but call V4L2_CID_GAIN for the condition
>> > > of setting total_gain=AGxDG.
>> >
>> > >How do you update the two other controls if the user updates the
>V4L2_CID_GAIN control?
>> >
>> > In imx208 driver:
>> >
>> > Add two pointers *digital_gain and *analog_gain of v4l2_ctrl in the global
>structure imx208.
>> > static int imx208_init_controls(struct imx208 *imx208) {
>> > Imx208->digital_gain = v4l2_ctrl_new_std(..., V4L2_CID_DIGITAL_GAIN,
>> > Imx208->...); analog_gain =
>> > Imx208->v4l2_ctrl_new_std(...,V4L2_CID_ANALOGUE_GAIN, ...);
>> >
>> > static int imx208_set_ctrl(struct v4l2_ctrl *ctrl) { ...
>> > 	case V4L2_CID_ANALOGUE_GAIN:
>> > 		ret = imx208_write_reg(imx208, IMX208_REG_ANALOG_GAIN, 2,
>ctrl->val);
>> > 		break;
>> > 	case V4L2_CID_DIGITAL_GAIN:
>> > 		ret = imx208_update_digital_gain(imx208, 2, ctrl->val);
>> > 		break;
>> > 	case V4L2_CID_ GAIN:
>> > 		ret = imx208_update_gain(imx208, 2, ctrl->val);  // total gain
>> > 		break;
>> > }
>> >
>> > Then the implementation of imx208_update_gain():
>> > static int imx208_update_gain(struct imx208 *imx208, u32 len, u32
>> > val) {
>> > 	digital_gain = (val - 1) / ag_max;
>> > 	digital_gain = map_to_real_DG(digital_gain);  		// map to 1x,
>2x, 4x, 8x, 16x
>> > 	digital_gain_code = digital_gain << 8			//  DGx256 for
>DG_code
>> > 	ret = imx208_update_digital_gain(imx208, 2, digital_gain_code);
>> > 	imx208->digital_gain->val = digital_gain_code;
>> > 	analog_gain = val/digital_gain;
>> > 	analog_gain_code = SMIA_AG_to_Code(analog_gain);  // AG =
>256/(256-ag_code)
>> > 	ret = imx208_write_reg(imx208, IMX208_REG_ANALOG_GAIN, 2,
>analog_gain_code);
>> > 	imx208->digital_gain->val = analog_gain_code;
>>
>> >How about putting this piece of code to the user space instead?
>>
>> >Some work would be needed to generalise it in order for it to work on other
>sensors that do need >digital gain applied, too --- assuming it'd be combined
>with the TRY_EXT_CTRLS rounding flags.
>>
>> There might be many kinds of discrete DG formats. For imx208, DG=2^n,
>> but for other sensors, DG could be 2*n, 5*n, or other styles. If HAL
>> needs to
>
>I guess the most common is multiplication and a bit shift (by e.g. 8), e.g.
>multiplying the value by a 16-bit number with a 8-bit fractional part. The
>imx208 apparently lacks the multiplication and only has the bit shift.
>
>Usually there's some sort of technical reason for the choice of the digital gain
>implementation and therefore I expect at least the vast majority of the
>implementations to be either of the two.

We shall ensure the expansibility of this architecture to include other kind of styles in the future. Is this API design architecture-wise ok?

>
>> cover all cases, kernel will have to update more information to this
>> control. Another problem is should HAL take over the SMIA calculation?
>> If so, kernel will also need to update SMIA parameters to user space
>> (or create an addition filed for SMIA in the configuration XML file).
>
>The parameters for the analogue gain model should come from the driver, yes.
>We do not have controls for that purpose but they can (and should) be added.
>

How about still follow PC's proposal to implement in XML? It was in IQ tuning file before which is in userspace. Even I proposed to PC to study with ICG SW team whether this info could be retrieved from 3A algorithm.

>--
>Regards,
>
>Sakari Ailus
>sakari.ailus@linux.intel.com