Date:   Tue, 17 May 2022 14:47:06 +0200
From:   Quentin Schulz <quentin.schulz@...obroma-systems.com>
To:     Jacopo Mondi <jacopo@...ndi.org>
Cc:     Quentin Schulz <foss+kernel@...il.net>, shawnx.tu@...el.com,
        mchehab@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-media@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] media: i2c: ov5675: add .get_selection support

Hi Jacopo,

On 5/17/22 13:18, Jacopo Mondi wrote:
> Hi Quentin
> 
> On Tue, May 17, 2022 at 11:25:17AM +0200, Quentin Schulz wrote:
>> Hi Jacopo,
>>
>> On 5/12/22 11:05, Jacopo Mondi wrote:
>>> Hi Quentin,
>>>
>>> On Mon, May 09, 2022 at 04:32:26PM +0200, Quentin Schulz wrote:
>>>> From: Quentin Schulz <quentin.schulz@...obroma-systems.com>
>>>>
>>>> The sensor has 2592*1944 active pixels, surrounded by 16 active dummy
>>>> pixels and there are an additional 24 black rows "at the bottom".
>>>>
>>>> As recommended in the SELECTION API documentation, let's put the first
>>>> useful active pixel at the top/left corner (0,0).
>>>>
>>>> This window is the default and maximal crop allowed by the sensor.
>>>>
>>>> Signed-off-by: Quentin Schulz <quentin.schulz@...obroma-systems.com>
>>>> ---
>>>>
>>>> added in v3
>>>>
>>>>    drivers/media/i2c/ov5675.c | 25 +++++++++++++++++++++++++
>>>>    1 file changed, 25 insertions(+)
>>>>
>>>> diff --git a/drivers/media/i2c/ov5675.c b/drivers/media/i2c/ov5675.c
>>>> index 5544e1ae444e..8e3a5bc6c027 100644
>>>> --- a/drivers/media/i2c/ov5675.c
>>>> +++ b/drivers/media/i2c/ov5675.c
>>>> @@ -78,6 +78,9 @@
>>>>    #define OV5675_REG_FORMAT1		0x3820
>>>>    #define OV5675_REG_FORMAT2		0x373d
>>>>
>>>> +#define OV5675_PIXEL_ARRAY_WIDTH	2592U
>>>> +#define OV5675_PIXEL_ARRAY_HEIGHT	1944U
>>>> +
>>>>    #define to_ov5675(_sd)			container_of(_sd, struct ov5675, sd)
>>>>
>>>>    static const char * const ov5675_supply_names[] = {
>>>> @@ -1115,6 +1118,27 @@ static int ov5675_get_format(struct v4l2_subdev *sd,
>>>>    	return 0;
>>>>    }
>>>>
>>>> +static int ov5675_get_selection(struct v4l2_subdev *sd,
>>>> +				struct v4l2_subdev_state *state,
>>>> +				struct v4l2_subdev_selection *sel)
>>>> +{
>>>> +	if (sel->which != V4L2_SUBDEV_FORMAT_ACTIVE)
>>>> +		return -EINVAL;
>>>> +
>>>> +	switch (sel->target) {
>>>> +	case V4L2_SEL_TGT_CROP:
>>>> +	case V4L2_SEL_TGT_CROP_DEFAULT:
>>>> +	case V4L2_SEL_TGT_CROP_BOUNDS:
>>>> +		/* In HW, top/left corner is actually at (16,16) */
>>>> +		sel->r.top = 0;
>>>> +		sel->r.left = 0;
>>>> +		sel->r.width = OV5675_PIXEL_ARRAY_WIDTH;
>>>> +		sel->r.height = OV5675_PIXEL_ARRAY_HEIGHT;
>>>> +		return 0;
>>>> +	}
>>>
>>> CROP_NATIVE = the full pixel array size = 2592x1944
>>>
>>> CROP_BOUNDS = the rectangle that contains all possible crop
>>>                 rectangles, aka the readable portion of your pixel array.
>>>                 If in your case the sensor can read out dummy and non
>>>                 active lines this is == NATIVE
>>>
>>> CROP_DEFAULT = the active/valid pixel area. If there are any
>>>                  dummy/invalid lines the DEFAULT rectangle should not
>>>                  include them
>>>
>>> CROP = the portion of the active pixel area cropped to produce the
>>>          final image. You should look into the modes definition and
>>>          inspect what values are programmed in register 0x380x (I don't
>>>          have a datasheet hence I don't know what corresponds to what)
>>>
>>> Does this make any sense to you ?
>>>
>>
>> It's difficult to make sense of the datasheet to be honest.
>>
> 
> Seems like it is made on purpose, isn't it :)
> 
> 
>> There's a 3296x2480px "full-size" rectangle, then the sensor array output
> 
> Are there that many blank/invalid lines/cols ?
> 

Seems very unlikely, but it's in the schema..

Can't rule out that they just reused the same schema they had for a 
bigger sensor and just didn't update the sizes for the full-size rectangle..

>> area called CROP and configurable through registers 0x380x, then another
>> output area called WIN (for window) also configurable through registers
>> 0x380x. The WIN area seems to be just a mask applied on top of CROP area
>> ("timing is not affected").
>>
>> On top of that, the schema shows 24 black lines - I assume - incorrectly,
>> one after the start of the full-size rectangle, one after the end of the
>> full-size rectangle.
>>
>> Then the sensor array area region in another section explicitly specifies
>> the sensor to be 2624x2000px, active dummy pixels (2 16-pixel rows and
>> columns) and black lines (1 24-pixel line) included. Which makes the actual
>> useful area 2592x1944px.
>>
>> In the datasheet, the default size for the CROP area is
>> 2624x1952px, offset (0,12) and for WIN it is 2592x1944px, offset (16,4)
>> (assumed relative to CROP given the second coordinate).
>>
>> In the kernel driver though, the 2592x1944px mode configures the CROP area
>> to be 2624x1968px offset (0,4) and the WIN area to be 2592x1944px, offset
>> (16,13).
>>
>> The datasheet only ever mentions 2592x1944px as being the max resolution of
>> the sensor though the sensor output area documentation and registers do not
>> mention such a limitation.
>>
>> Since we're not modifying the crop area at the moment, CROP_DEFAULT and CROP
>> would be the same, which would both be 2592x1944px.
>>
>> For the two others, I'm not sure. Any clue or hint with the info I just
>> gave?
> 
> Is my intrpretation of the above correct ?
> 
>                       [2624]
>          +------------------------------+
>          |     |     16 dummy     |     |
>          |------------------------------|
>          |     |                  |     |
>          |     |     [2592]       |     |
>          |     |                  |     |
>          |16   |      valid       | 16  |[2000]
>          |dummy|                  |dummy|
>          |     |            [1944]|     |
>          |     |                  |     |
>          |------------------------------|
>          |     |     24 blacks    |     |
>          |------------------------------|
>          |     |     16 dummy     |     |
>          -------------------------------|
> 

the 24 black lines and 16 dummy pixels rows at the bottom are swapped, 
but otherwise yes.

BTW, did you use a specific tool to make this schema?

> 
> Math looks right at least:
> 
>          2000 - 16 - 24 - 16 = 1944
>          2624 - 16 - 16 = 2592
> 
> As V4L2 selection targets are defined in respect to they larger
> sourrounding target, if the documentation about the full size array
> (3296,2480) doesn't tell you what offset the readable part is, I think
> it's fair to define
>          - NATIVE == BOUNDS = (0, 0, 2624, 2000)
>          - DEFAULT == CROP = (16, 16, 2592, 1944)
> 
> Or maybe better not define NATIVE at all.
> 
> The skipped rows/cols almost seems to match what the datasheet suggests by
> combining the cropping and windowing rectangles top/left offsets (with
> 2 cols more skipped compared to my understanding)
> 
>          crop = (0, 12, 2624, 1952)
>          win = (16, 6, 2592, 1944)
> 
>          CROP = (16, 18, 2592, 1944)
> 
> The driver does that a little differently with:
> 
>          crop = (0, 4, 2624, 1968)
>          win = (16, 13, 2592, 1944)
> 
>          CROP = (16, 17, 2624, 1944)
> 
> Which seems a little off as the driver values for the VTS and HTS
> register counts from 0 hence it seems to be skipping 17 rows and 18
> cols (maybe the driver adjusts when writing the values to registers ?)
> 

Datasheet states that whatever the window, it'll reuse the timings of 
the crop ("Windowing is achieved by masking off the pixels outside of 
the window; thus, the original timing is not affected."). So I assume 
what matters it that the timings are right for the crop.

> If you feel like it you can try to adjust the driver rectangles, but
> in my experience subtle regressions might be introduced by moving
> those values, hence I would not be too concerned and just report
> whatever the driver does. I assume you're doing this in the context of
> pleasing libcamera requirements, and as much as I don't like saying
> this, if we're 1 or 2 columns off when reporting the CROP rectangle,
> it's not a huge issue.
> 

Yes, this patch is for satisfying libcamera requirements.

I also just saw that we actually support two modes for the sensor. So 
I'll need to get the width and height of the currently selected 
supported_modes. Fortunately, the window+crop offsets seem identical so 
there's no need to add some logic for those.

I'll resend patch 3 and 4 separately so they can be merged and I'll 
continue fighting with runtime PM on our camera sensor, looking into HW 
if something's off there.

Cheers,
Quentin

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