On 15/12/16 18:51, Shuah Khan wrote:
On 12/15/2016 10:25 AM, Mauro Carvalho Chehab wrote:
Em Thu, 15 Dec 2016 10:09:53 -0700
Shuah Khan <shuahkh@xxxxxxxxxxxxxxx> escreveu:
On 12/15/2016 09:28 AM, Hans Verkuil wrote:
On 15/12/16 17:06, Shuah Khan wrote:
I think this will work for interface entities, but for subdev entities this
certainly won't work. Unbinding subdevs should be blocked (just set
suppress_bind_attrs to true in all subdev drivers). Most top-level drivers
have pointers to subdev data, so unbinding them will just fail horribly.
Yes that is an option. I did something similar for au0828 and snd_usb_audio
case, so the module that registers the media_device can't unbound until the
other driver. If au0828 registers media_device, it becomes the owner and if
it gets unbound ioctls will start to see problems.
Sorry I meant to say rmmod'ed not unbound. Unbound will work just fine. If the
modules that owns the media_devnode goes away, there will be problems with
cdev trying to load module when application closes the device file and exits.
In this case, Media Device Allocator API takes module reference, so its use
count goes up.
What this means though is that drivers can't be unbound easily. But that is
a small price to pay compared to the problems we will see if a driver is
unbound when its entities are still in use. Also, unsetting bind_attrs has
to be done as well, otherwise we can never unbind any driver.
I don't think suppress_bind_attrs will work on USB drivers, as the
device can be physically removed.
Yeah setting suppress_bind_attrs would cause problems. On one hand keeping
all entities until all references are gone sound like a good option, however
this would cause problems coordinating removal especially in the case of
embedded entities. Can this be done in a simpler way? The way I see it, we
have /dev/video, /dev/dvb, /dev/snd/* etc. that depend on /dev/media for
graph nodes. Any one of these devices could be open when any of the drivers
is unbound (physical removal is a simpler case).
Would it make sense to enforce that dependency. Can we tie /dev/media usecount
to /dev/video etc. usecount? In other words:
/dev/video is opened, then open /dev/media.
When a device node is registered it should increase the refcount on the media_device
(as I proposed, that would be mdev->dev). When a device node is unregistered and the
last user disappeared, then it can decrease the media_device refcount.
So as long as anyone is using a device node, the media_device will stick around as
well.
No need to take refcounts on open/close.
One note: as I mentioned, the video_device does not set the cdev parent correctly,
so that bug needs to be fixed first for this to work.
prevent entities being removed if /dev/media is open.
Would that help. The above could be done in a generic way possibly. Would it
help if /dev/media is kept open when streaming is active? That is just one
Again, it's not about the device nodes, it's about the media_device.
Regards,
Hans
use-case, there might be others.
thanks,
-- Shuah
thanks,
-- Shuah
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