Re: [PATCH 0/2] Use Media Dev Allocator to fix vimc dev lifetime bugs

[Shuah Khan]

On 6/13/19 7:24 AM, Helen Koike wrote:
> On 6/13/19 2:44 AM, Hans Verkuil wrote:
> > On 5/24/19 5:31 AM, Shuah Khan wrote:
> > > media_device is embedded in struct vimc_device and when vimc is removed
> > > vimc_device and the embedded media_device goes with it, while the active
> > > stream and vimc_capture continue to access it.
> > >
> > > Fix the media_device lifetime problem by changing vimc to create shared
> > > media_device using Media Device Allocator API and vimc_capture getting
> > > a reference to vimc module. With this change, vimc module can be removed
> > > only when the references are gone. vimc can be removed after vimc_capture
> > > is removed.
> > >
> > > Media Device Allocator API supports just USB devices. Enhance it
> > > adding a genetic device allocate interface to support other media
> > > drivers.
> > >
> > > The new interface takes pointer to struct device instead and creates
> > > media device. This interface allows a group of drivers that have a
> > > common root device to share media device resource and ensure media
> > > device doesn't get deleted as long as one of the drivers holds its
> > > reference.
> > >
> > > The new interface has been tested with vimc component driver to fix
> > > panics when vimc module is removed while streaming is in progress.
> >
> > Helen, can you review this series? I'm not sure this is the right approach
> > for a driver like vimc, and even if it is, then it is odd that vimc-capture
> > is the only vimc module that's handled here.
>
> Hi Hans,
>
> Yes, I can take a look. Sorry, I've been a bit busy these days but I'll
> try to take a look at this patch series (and the others) asap.
>
> Helen
>
> > My gut feeling is that this should be handled inside vimc directly and not
> > using the media-dev-allocator.

Hi Hans and Helen,

I explored fixing the problem within vimc before I went down the path to
use Media Device Allocator API. I do think that it is cleaner to go this
way and easier to maintain.

vimc is a group pf component drivers that rely on the media device vimc
in vimc and falls into the use-case Media Device Allocator API is added
to address. The release and life-time management happens without vimc
component drivers being changed other than using the API to get and put
media device reference.

thanks,
-- Shuah