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SubjectRe: [PATCH v6 4/4] media: i2c: ov5675: add .get_selection support
From
Jacopo, Tommaso,

On 6/8/22 08:42, Jacopo Mondi wrote:
> Hi
>
> On Wed, Jun 08, 2022 at 12:04:05AM +0200, Tommaso Merciai wrote:
>> Hi Quentin/Jacopo,
>>
>> On Tue, Jun 07, 2022 at 06:51:36PM +0200, Jacopo Mondi wrote:
>>> Hi Quentin,
>>>
>>> On Tue, Jun 07, 2022 at 05:33:35PM +0200, Quentin Schulz wrote:
>>>> From: Quentin Schulz <quentin.schulz@theobroma-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".
>>>>
>>>> [2624]
>>>> +-----+------------------+-----+
>>>> | | 16 dummy | |
>>>> +-----+------------------+-----+
>>>> | | | |
>>>> | | [2592] | |
>>>> | | | |
>>>> |16 | valid | 16 |[2000]
>>>> |dummy| |dummy|
>>>> | | [1944]| |
>>>> | | | |
>>>> +-----+------------------+-----+
>>>> | | 16 dummy | |
>>>> +-----+------------------+-----+
>>>> | | 24 black lines | |
>>>> +-----+------------------+-----+
>>>>
>>>> The top-left coordinate is gotten from the registers specified in the
>>>> modes which are identical for both currently supported modes.
>>>>
>>>> There are currently two modes supported by this driver: 2592*1944 and
>>>> 1296*972. The second mode is obtained thanks to subsampling while
>>>> keeping the same field of view (FoV). No cropping involved, hence the
>>>> harcoded values.
>>>>
>>>> Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
>>>> ---
>>>>
>>>> v6:
>>>> - explicit a bit more the commit log around subsampling for lower
>>>> resolution modes,
>>>> - (again) fixed reporting for V4L2_SEL_TGT_CROP_* thanks to Jacopo's help,
>>>>
>>>> v4:
>>>> - explicit a bit more the commit log,
>>>> - added drawing in the commit log,
>>>> - fixed reporting for V4L2_SEL_TGT_CROP_* thanks to Jacopo's help,
>>>>
>>>> added in v3
>>>>
>>>> drivers/media/i2c/ov5675.c | 21 +++++++++++++++++++++
>>>> 1 file changed, 21 insertions(+)
>>>>
>>>> diff --git a/drivers/media/i2c/ov5675.c b/drivers/media/i2c/ov5675.c
>>>> index 80840ad7bbb0..2230ff47ef49 100644
>>>> --- a/drivers/media/i2c/ov5675.c
>>>> +++ b/drivers/media/i2c/ov5675.c
>>>> @@ -1121,6 +1121,26 @@ 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_BOUNDS:
>>>
>>> Seem like we have trouble understanding each other, or better, I have
>>> troubles explaining myself most probably :)
>>>
>>> If the dummy/black area is readable, this should just be (0, 0, 2624,
>>> 2000) like it was in your previous version. What has changed that I
>>> have missed ?
>>

I wouldn't say there's some misunderstanding, it's just super hard to
figure out how to match what the datasheet says to what the kernel
wants. Yay to obscure/confusing datasheets \o/

I just did things too quickly, nothing changed. Sorry, will send a v7.

>> Taking as reference drivers/media/i2c/ov5693.c and others,
>> seems ok what Quentin have done from my side.
>>
>> Just one thing: maybe is better to avoid magic numbers with more
>> explicit defines like:
>>
>> + case V4L2_SEL_TGT_CROP_DEFAULT:
>> + sel->r.top = OV5675_ACTIVE_START_TOP;
>> + sel->r.left = OV5693_ACTIVE_START_LEFT;
>> + sel->r.width = OV5693_ACTIVE_WIDTH;
>> + sel->r.height = OV5693_ACTIVE_HEIGHT;
>>

They are hardcoded today but actually depend on what;s set in the
registers too, which might differ if we add more modes in the future?
It's anyway auto-magic and it's the only place it's used, so not sure it
brings much especially since the variable names on the left hand side of
the operator are pretty self-explanatory (not talking about
V4L2_SEL_TGT_CROP_* :p)? Not that I'm against it.

Cheers,
Quentin

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