Re: [PATCH v2] [media] media-device: use kref for media_device instance

[Shuah Khan <shuahkh@osg.samsung.com>]

On 03/21/2016 05:10 AM, Laurent Pinchart wrote:
> Hi Mauro,
> 
> Thank you for the patch.
> 
> On Friday 18 Mar 2016 21:42:16 Mauro Carvalho Chehab wrote:
>> Now that the media_device can be used by multiple drivers,
>> via devres, we need to be sure that it will be dropped only
>> when all drivers stop using it.
> 
> I've discussed this with Shuah previously and I'm surprised to see that the 
> problem hasn't been fixed : using devres for this purpose is just plain wrong. 
> The empty media_device_release_devres() function should have given you a hint.
> 
> What we need instead is a list of media devices indexed by struct device (for 
> this use case) or by struct device_node (for DT use cases). It will both 
> simplify the code and get rid of the devres abuse.
> 
> Shuah, if I recall correctly you worked on implementing such a solution after 
> our last discussion on the topic. Could you please update us on the status ?
> 

It is work in progress. I have a working prototype for au0828 which is an easier
case. I am working on resolving a couple of issues to differentiate media devices
allocated using the global media device list vs. the ones embedded in the driver
data structures. We have many of those.

I had to put this work on the back burner to get the au0882 and snd-usb-audio
wrapped up. I can get the RFC patches on top of the au0882 and snd-usb-audio.
We can discuss them at the upcoming media summit.

> In the mean time, let's hold off on this patch, and merge a proper solution 
> instead.

I think Mauro's restructure helps us with such differentiation and it will be
easy enough to change out devres to get media get API.

thanks,
-- Shuah

-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978