From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Brian Starkey <Brian.Starkey@arm.com>, nd <nd@arm.com>,
David Airlie <airlied@linux.ie>,
Liviu Dudau <Liviu.Dudau@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"james qian wang (Arm Technology China)"
<james.qian.wang@arm.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
Mihail Atanassov <Mihail.Atanassov@arm.com>,
Sean Paul <sean@poorly.run>
Subject: Re: [RFC,3/3] drm/komeda: Allow non-component drm_bridge only endpoints
Date: Tue, 22 Oct 2019 09:48:26 +0100 [thread overview]
Message-ID: <20191022084826.GP25745@shell.armlinux.org.uk> (raw)
In-Reply-To: <20191022084210.GX11828@phenom.ffwll.local>
On Tue, Oct 22, 2019 at 10:42:10AM +0200, Daniel Vetter wrote:
> 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.
>
> I think the only patches that existed where for panel, and we only
> discussed the bridge case. At least I can only find patches for panel,not
> bridge, but might be missing something.
I had a patches, which is why I raised the problem with the core:
6961edfee26d bridge hacks using device links
but it never went further than an experiment at the time because of the
problems in the core. As it was a hack, it never got posted. Seems
that kernel tree (for the cubox) is still 5.2 based, so has a lot of
patches and might need updating to a more recent base before anything
can be tested.
--
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
next prev parent reply other threads:[~2019-10-22 8:48 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 14:34 [PATCH 0/3] drm/komeda: Support for drm_bridge endpoints Mihail Atanassov
2019-10-04 14:34 ` [PATCH 1/3] drm/komeda: Consolidate struct komeda_drv allocations Mihail Atanassov
2019-10-04 14:34 ` [PATCH 2/3] drm/komeda: Memory manage struct komeda_drv in probe/remove Mihail Atanassov
2019-10-04 14:34 ` [RFC PATCH 3/3] drm/komeda: Allow non-component drm_bridge only endpoints Mihail Atanassov
2019-10-09 5:54 ` [RFC,3/3] " james qian wang (Arm Technology China)
2019-10-16 15:51 ` Mihail Atanassov
2019-10-16 16:22 ` Brian Starkey
2019-10-17 3:07 ` james qian wang (Arm Technology China)
2019-10-17 8:20 ` Brian Starkey
2019-10-17 10:21 ` james qian wang (Arm Technology China)
2019-10-17 10:48 ` Brian Starkey
2019-10-17 11:41 ` Russell King - ARM Linux admin
2019-10-18 6:57 ` james qian wang (Arm Technology China)
2019-10-18 9:12 ` Brian Starkey
2019-10-22 8:42 ` Daniel Vetter
2019-10-22 8:48 ` Russell King - ARM Linux admin [this message]
2019-10-22 8:50 ` Daniel Vetter
2019-10-22 14:42 ` Russell King - ARM Linux admin
2019-10-22 14:53 ` Russell King - ARM Linux admin
2019-10-24 8:03 ` Mihail Atanassov
2019-10-24 5:21 ` james qian wang (Arm Technology China)
2019-10-18 6:38 ` james qian wang (Arm Technology China)
2019-10-18 11:01 ` Mihail Atanassov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191022084826.GP25745@shell.armlinux.org.uk \
--to=linux@armlinux.org.uk \
--cc=Brian.Starkey@arm.com \
--cc=Liviu.Dudau@arm.com \
--cc=Mihail.Atanassov@arm.com \
--cc=airlied@linux.ie \
--cc=daniel@ffwll.ch \
--cc=dri-devel@lists.freedesktop.org \
--cc=james.qian.wang@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=nd@arm.com \
--cc=sean@poorly.run \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).