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    SubjectRe: [RFC,3/3] drm/komeda: Allow non-component drm_bridge only endpoints
    On Thu, Oct 17, 2019 at 10:48:12AM +0000, Brian Starkey wrote:
    > On Thu, Oct 17, 2019 at 10:21:03AM +0000, james qian wang (Arm Technology China) wrote:
    > > On Thu, Oct 17, 2019 at 08:20:56AM +0000, Brian Starkey wrote:
    > > > On Thu, Oct 17, 2019 at 03:07:59AM +0000, james qian wang (Arm Technology China) wrote:
    > > > > On Wed, Oct 16, 2019 at 04:22:07PM +0000, Brian Starkey wrote:
    > > > > >
    > > > > > If James is strongly against merging this, maybe we just swap
    > > > > > wholesale to bridge? But for me, the pragmatic approach would be this
    > > > > > stop-gap.
    > > > > >
    > > > >
    > > > > This is a good idea, and I vote +ULONG_MAX :)
    > > > >
    > > > > and I also checked tda998x driver, it supports bridge. so swap the
    > > > > wholesale to brige is perfect. :)
    > > > >
    > > >
    > > > Well, as Mihail wrote, it's definitely not perfect.
    > > >
    > > > Today, if you rmmod tda998x with the DPU driver still loaded,
    > > > everything will be unbound gracefully.
    > > >
    > > > If we swap to bridge, then rmmod'ing tda998x (or any other bridge
    > > > driver the DPU is using) with the DPU driver still loaded will result
    > > > in a crash.
    > >
    > > I haven't read the bridge code, but seems this is a bug of drm_bridge,
    > > since if the bridge is still in using by others, the rmmod should fail
    > >
    >
    > Correct, but there's no fix for that today. You can also take a look
    > at the thread linked from Mihail's cover letter.
    >
    > > And personally opinion, if the bridge doesn't handle the dependence.
    > > for us:
    > >
    > > - add such support to bridge
    >
    > That would certainly be helpful. I don't know if there's consensus on
    > how to do that.
    >
    > > or
    > > - just do the insmod/rmmod in correct order.
    > >
    > > > So, there really are proper benefits to sticking with the component
    > > > code for tda998x, which is why I'd like to understand why you're so
    > > > against this patch?
    > > >
    > >
    > > This change handles two different connectors in komeda internally, compare
    > > with one interface, it increases the complexity, more risk of bug and more
    > > cost of maintainance.
    > >
    >
    > Well, it's only about how to bind the drivers - two different methods
    > of binding, not two different connectors. I would argue that carrying
    > our out-of-tree patches to support both platforms is a larger
    > maintenance burden.
    >
    > Honestly this looks like a win-win to me. We get the superior approach
    > when its supported, and still get to support bridges which are more
    > common.
    >
    > As/when improvements are made to the bridge code we can remove the
    > component bits and not lose anything.

    There was an idea a while back about using the device links code to
    solve the bridge issue - but at the time the device links code wasn't
    up to the job. I think that's been resolved now, but I haven't been
    able to confirm it. I did propose some patches for bridge at the
    time but they probably need updating.

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