linux-kernel - Re: [PATCH v15 18/19] media: uvcvideo: implement UVC v1.5 ROI

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Message-ID: <8151585c-cb4c-424d-a81c-939ee30d8e9d@redhat.com>
Date: Mon, 18 Nov 2024 16:59:19 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: Ricardo Ribalda <ribalda@...omium.org>, Gergo Koteles <soyer@....hu>
Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Ricardo Ribalda <ribalda@...nel.org>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Hans Verkuil <hverkuil@...all.nl>, Yunke Cao <yunkec@...omium.org>,
 linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
 Yunke Cao <yunkec@...gle.com>
Subject: Re: [PATCH v15 18/19] media: uvcvideo: implement UVC v1.5 ROI

Hi Ricardo,

On 14-Nov-24 9:03 PM, Ricardo Ribalda wrote:
> Hi Gergo
> 
> Sorry, I forgot to reply to your comment in v14.
> 
> On Thu, 14 Nov 2024 at 20:53, Gergo Koteles <soyer@....hu> wrote:
>>
>> Hi Ricardo,
>>
>> On Thu, 2024-11-14 at 19:10 +0000, Ricardo Ribalda wrote:
>>>
>>> +     },
>>> +     {
>>> +             .id             = V4L2_CID_UVC_REGION_OF_INTEREST_AUTO,
>>> +             .entity         = UVC_GUID_UVC_CAMERA,
>>> +             .selector       = UVC_CT_REGION_OF_INTEREST_CONTROL,
>>> +             .size           = 16,
>>> +             .offset         = 64,
>>> +             .v4l2_type      = V4L2_CTRL_TYPE_BITMASK,
>>> +             .data_type      = UVC_CTRL_DATA_TYPE_BITMASK,
>>> +             .name           = "Region Of Interest Auto Controls",
>>> +     },
>>>  };
>>>
>>
>> Wouldn't be better to use 8 V4L2_CTRL_TYPE_BOOLEAN controls for this?
> 
> If I create 8 Booleans, they will always be shown in the device. And
> the user will not have a way to know which values are available and
> which are not.
> 
> We will also fail the v4l2-compliance test, because there will be up
> to 7 boolean controls that will not be able to be set to 1, eventhough
> they are writable.

So why can't these other controls be set to 1? Because only one
of the options in the bitmask can be selected at a time ?

If only 1 bit in the UVC_CTRL_DATA_TYPE_BITMASK for this can be one
at the time, then this should be mapped to a V4L2_CTRL_TYPE_MENU
just like how that is done for V4L2_CID_EXPOSURE_AUTO already.

Actually looking at existing comments about UVC_CTRL_DATA_TYPE_BITMASK
in the driver there is this comment on top of uvc_mapping_get_menu_value()

 * For controls of type UVC_CTRL_DATA_TYPE_BITMASK, the UVC control value is
 * expressed as a bitmask and is thus guaranteed to have a single bit set.

Assuming this "guaranteed to have a single bit set" comment is valid for
the V4L2_CID_UVC_REGION_OF_INTEREST_AUTO part of UVC_CT_REGION_OF_INTEREST_CONTROL
too then I think we should simply map this to a menu similar to how
this is done for V4L2_CID_EXPOSURE_AUTO.

Note V4L2_CID_EXPOSURE_AUTO is the only existing user of UVC_CTRL_DATA_TYPE_BITMASK
at the moment.

Mapping this to a menu should nicely address Gergo's concerns here.

Regards,

Hans