Re: [RFC 00/19] Async sub-notifiers and how to use them

Hans Verkuil
2017-08-23T12:02:31Z

On 08/23/17 13:34, Pavel Machek wrote:
> Hi!
>
>>>> Is this always the case? In the R-Car VIN driver I register the video
>>>> devices using video_register_device() in the complete handler. Am I
>>>> doing things wrong in that driver? I had a patch where I moved the
>>>> video_register_device() call to probe time but it got shoot down in
>>>> review and was dropped.
>>>
>>> I don't think the current implementation is wrong, it's just different
>>> from other drivers; there's really no requirement regarding this AFAIU.
>>> It's one of the things where no attention has been paid I presume.
>>
>> It actually is a requirement: when a device node appears applications can
>> reasonably expect to have a fully functioning device. True for any device
>> node. You don't want to have to wait until some unspecified time before
>> the full functionality is there.
>
> Well... /dev/sdb appears, but you still get -ENOMEDIA before user
> presses "Turn on USB storage" button on android phone.
>
> So I agree it is not desirable, but it sometimes happens.

But that is expected behavior. There is nothing wrong with the device.
Just as it is expected behavior that you can't stream from a video node
if there is no HDMI source connected.

That the HDMI receiver or sensor itself is completely missing is quite
another story, though.

Regards,

Hans