linux-kernel - Re: [RFC 3/5] media: v4l2-ctrls: Add support for V4L2_CID

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Date:   Thu, 15 Aug 2019 15:41:53 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Jacopo Mondi <jacopo@...ndi.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "open list:MEDIA INPUT INFRASTRUCTURE (V4L/DVB)" 
        <linux-media@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 3/5] media: v4l2-ctrls: Add support for V4L2_CID_LOCATION

On 8/15/19 3:02 PM, Jacopo Mondi wrote:
> Hi Laurent,
> 
> On Thu, Aug 15, 2019 at 01:53:53AM +0300, Laurent Pinchart wrote:
>> Hi Jacopo,
>>
>> Thank you for the patch.
>>
>> On Wed, Aug 14, 2019 at 10:28:13PM +0200, Jacopo Mondi wrote:
>>> Add support for the newly defined V4L2_CID_LOCATION read-only control
>>> used to report the camera device mounting position.
>>>
>>> Signed-off-by: Jacopo Mondi <jacopo@...ndi.org>
>>> ---
>>>  drivers/media/v4l2-core/v4l2-ctrls.c | 7 +++++++
>>>  include/uapi/linux/v4l2-controls.h   | 4 ++++
>>>  2 files changed, 11 insertions(+)
>>>
>>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
>>> index 7d3a33258748..8ab0857df59a 100644
>>> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
>>> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
>>> @@ -943,6 +943,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>>>  	case V4L2_CID_AUTO_FOCUS_RANGE:		return "Auto Focus, Range";
>>>  	case V4L2_CID_PAN_SPEED:		return "Pan, Speed";
>>>  	case V4L2_CID_TILT_SPEED:		return "Tilt, Speed";
>>> +	case V4L2_CID_LOCATION:			return "Location";
>>
>> Depending on what we decide to name the control (see review of 2/5), you
>> should adjust the description accordingly.
>>
>>>
>>>  	/* FM Radio Modulator controls */
>>>  	/* Keep the order of the 'case's the same as in v4l2-controls.h! */
>>> @@ -1300,6 +1301,12 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>>>  		break;
>>>  	case V4L2_CID_MPEG_VIDEO_FWHT_PARAMS:
>>>  		*type = V4L2_CTRL_TYPE_FWHT_PARAMS;
>>> +	case V4L2_CID_LOCATION:
>>> +		*type = V4L2_CTRL_TYPE_INTEGER;
>>> +		*flags |= V4L2_CTRL_FLAG_READ_ONLY;
>>> +		*min = V4L2_LOCATION_FRONT;
>>> +		*max = V4L2_LOCATION_BACK;
>>
>> I don't think the control should have a min and a max different than the
>> current value, as it's a fully static control. I'd drop those two lines
>> here, and drivers will have to set value = min = max = V4L2_LOCATION_xxx
>> when creating the control. That why you should be able to collapse this
>> with V4L2_CID_MIN_BUFFERS_FOR_OUTPUT.
>>
> 
> Ah, I thought min/max should report the actual control values limits.
> Anyway, if we move this to be an integer menu control with an helper
> to parse the DT property and register the control on behalf of
> drivers, this will change.
> 
>>> +		*step = 1;
>>>  		break;
>>>  	default:
>>>  		*type = V4L2_CTRL_TYPE_INTEGER;
>>> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
>>> index 37807f23231e..5c4c7b245921 100644
>>> --- a/include/uapi/linux/v4l2-controls.h
>>> +++ b/include/uapi/linux/v4l2-controls.h
>>> @@ -889,6 +889,10 @@ enum v4l2_auto_focus_range {
>>>  #define V4L2_CID_PAN_SPEED			(V4L2_CID_CAMERA_CLASS_BASE+32)
>>>  #define V4L2_CID_TILT_SPEED			(V4L2_CID_CAMERA_CLASS_BASE+33)
>>>
>>> +#define V4L2_CID_LOCATION			(V4L2_CID_CAMERA_CLASS_BASE+34)
>>> +#define V4L2_LOCATION_FRONT			(0 << 0)
>>> +#define V4L2_LOCATION_BACK			(1 << 0)
>>
>> Why not just 0 and 1 ?
> 
> Or why not BIT(). I saw that the (1 << x) style is the mostly used one in
> this header file when defining macros like this one so I went for
> consistency with the existing code.

Definitely not right. This is an enumeration, so just number from 0, 1, 2, ...

Nothing to do with bits/bitmasks.

Regards,

	Hans

> 
>>
>>> +
>>>  /* FM Modulator class control IDs */
>>>
>>>  #define V4L2_CID_FM_TX_CLASS_BASE		(V4L2_CTRL_CLASS_FM_TX | 0x900)
>>
>> --
>> Regards,
>>
>> Laurent Pinchart