[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20191018065657.GA19117@jamwan02-TSP300>
Date: Fri, 18 Oct 2019 06:57:05 +0000
From: "james qian wang (Arm Technology China)" <james.qian.wang@....com>
To: Russell King - ARM Linux admin <linux@...linux.org.uk>
CC: Brian Starkey <Brian.Starkey@....com>,
Mihail Atanassov <Mihail.Atanassov@....com>,
"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
David Airlie <airlied@...ux.ie>,
Liviu Dudau <Liviu.Dudau@....com>,
Maxime Ripard <mripard@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
nd <nd@....com>, Sean Paul <sean@...rly.run>
Subject: Re: [RFC,3/3] drm/komeda: Allow non-component drm_bridge only
endpoints
On Thu, Oct 17, 2019 at 12:41:37PM +0100, Russell King - ARM Linux admin wrote:
> 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.
Hi Russell:
Thank you, that's a good news.
Hi Brian:
Can this convince you to fully swap to bridge ?
Actually even there is no fix, we won't real encounter such rmmod problem,
since we always build the bridge/tda998 (by Y) into the image.
Thanks
James
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
> According to speedtest.net: 11.9Mbps down 500kbps up
Powered by blists - more mailing lists