linux-kernel - Re: [PATCH v6 5/5] drivers: media: platform: Add NPCM Video Capture/Encode Engine driver

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Date:   Mon, 7 Nov 2022 09:23:41 +0100
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Kun-Fa Lin <milkfafa@...il.com>
Cc:     mchehab@...nel.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, openbmc@...ts.ozlabs.org,
        avifishman70@...il.com, tmaimon77@...il.com, tali.perry1@...il.com,
        kwliu@...oton.com, kflin@...oton.com
Subject: Re: [PATCH v6 5/5] drivers: media: platform: Add NPCM Video
 Capture/Encode Engine driver

On 07/11/2022 08:20, Kun-Fa Lin wrote:
> Hi Hans,
> 
> Thanks for the review.
> 
>>
>> These functions are not usually present when capturing from video. You don't
>> have a choice w.r.t. resolution and fps, since that's determined by the
>> incoming video. I would drop support for this.
> 
> Just to confirm, do you mean `npcm_video_enum_framesizes` and
> `npcm_video_enum_frameintervals` functions?

Right.

> 
> 
>>> +     switch (ctrl->id) {
>>> +     case V4L2_CID_DETECT_MD_MODE:
>>> +             if (ctrl->val == V4L2_DETECT_MD_MODE_GLOBAL)
>>> +                     video->ctrl_cmd = VCD_CMD_OPERATION_CAPTURE;
>>> +             else
>>> +                     video->ctrl_cmd = VCD_CMD_OPERATION_COMPARE;
>>> +     break;
>>
>> Incorrect indentation for the 'break'.
> 
> Will correct it.
> 
> 
>>> +     v4l2_ctrl_new_std_menu(&video->ctrl_handler, &npcm_video_ctrl_ops,
>>> +                            V4L2_CID_DETECT_MD_MODE,
>>> +                            V4L2_DETECT_MD_MODE_REGION_GRID, 0,
>>> +                            V4L2_DETECT_MD_MODE_GLOBAL);
>>
>> Why is this driver using a control designed for motion detection devices?
>> That seems odd, and it looks like you are abusing this control to do something
>> else.
> 
> The Video Capture/Differentiation (VCD) engine supports two modes:
> - COMPLETE (capture the next "complete frame" into memory)
> - DIFF (compare the incoming frame with the frame stored in memory,
> and updates the "diff frame" in memory)
> 
> The purpose here is to provide a way for application to switch the
> COMPLETE/DIFF mode. Since I couldn't find an appropriate ioctl that is
> designed for this purpose, so I used VIDIOC_S_CTRL with control values
> of V4L2_DETECT_MD_MODE_GLOBAL (for COMPLETE) and
> V4L2_DETECT_MD_MODE_REGION_GRID (for DIFF). It would be appreciated if
> you could point me in the right direction.

This is very much a driver-specific control. So you have to make your
own.

This series is a good example on how to add a custom control:

https://lore.kernel.org/linux-media/20221028023554.928-1-jammy_huang@aspeedtech.com/

Driver-specific controls are fine, as long as they are properly documented.

> 
> 
>> When you post v7, please also include the output of v4l2-compliance to the
>> cover letter!
>> Make sure you compile v4l2-compliance from the v4l-utils git repo, do not
>> use a version from a distro, that will be too old.
> 
> OK, I'll try to compile v4l2-compliance and include the output.
> 
> Regards,
> Marvin

Regards,

	Hans