Re: [PATCH] media: em28xx: fix inverted tuner capability check for VBI device

[Bradford Love]

Hi Christopher,

Just a couple days ago I plugged in one of our products with video/vbi
and no tuner and saw this message. I had not gotten around to fixing
it though. Thank you for catching this and submitting a patch.

Regards,

Bradford


Reviewed-by: Bradford Love <brad@xxxxxxxxxxxxxxxx>


On Tue, Sep 29, 2026 at 9:01 PM Christopher Snowhill <chris@xxxxxxxxxx> wrote:
>
> Commit 8e53399c63c3 ("media: em28xx: Add support for Empia em2828X
> bridge") changed the condition for setting V4L2_CAP_TUNER on the VBI
> device from "dev->tuner_type != TUNER_ABSENT" to a check of the video
> device's capabilities, but inverted it: the VBI node now advertises a
> tuner only when the video node does not have one.
>
> On boards without a tuner (e.g. the MyGica iGrabber, card=105) the VBI
> device's device_caps therefore contain V4L2_CAP_TUNER, while the shared
> vidioc_querycap() correctly omits it from cap->capabilities. This trips
> the sanity check in v4l_querycap() whenever the VBI node is queried,
> for example by udev's v4l_id on every hotplug:
>
>   WARNING: drivers/media/v4l2-core/v4l2-ioctl.c:1119 at v4l_querycap+0xff/0x110 [videodev]
>   (cap->capabilities & (vfd->device_caps | V4L2_CAP_DEVICE_CAPS)) != (vfd->device_caps | V4L2_CAP_DEVICE_CAPS)
>
> It also leaves the tuner ioctls enabled on the VBI node of tuner-less
> boards and disables them on boards that do have a tuner.
>
> Restore the intended logic so the VBI device has V4L2_CAP_TUNER exactly
> when the video device does.
>
> Fixes: 8e53399c63c3 ("media: em28xx: Add support for Empia em2828X bridge")
> Assisted-by: LLM
> Signed-off-by: Christopher Snowhill <chris@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
>  drivers/media/usb/em28xx/em28xx-video.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/usb/em28xx/em28xx-video.c b/drivers/media/usb/em28xx/em28xx-video.c
> index c418add65bb5..cdf1dc692b08 100644
> --- a/drivers/media/usb/em28xx/em28xx-video.c
> +++ b/drivers/media/usb/em28xx/em28xx-video.c
> @@ -3001,7 +3001,7 @@ static int em28xx_v4l2_init(struct em28xx *dev)
>                 v4l2->vbi_dev.queue->lock = &v4l2->vb_vbi_queue_lock;
>                 v4l2->vbi_dev.device_caps = V4L2_CAP_STREAMING |
>                         V4L2_CAP_READWRITE | V4L2_CAP_VBI_CAPTURE;
> -               if ((v4l2->vdev.device_caps & V4L2_CAP_TUNER) == 0)
> +               if (v4l2->vdev.device_caps & V4L2_CAP_TUNER)
>                         v4l2->vbi_dev.device_caps |= V4L2_CAP_TUNER;
>
>                 /* disable inapplicable ioctls */
> --
> 2.55.0
>